Electronic control system for powershift transmission with compensation for variation in supply voltage

ABSTRACT

A microprocessor-based electronic control system for a powershift transmission having at least one proportional actuator, such as a solenoid-operated proportional valve, is disclosed. The controller operates a plurality of on-off solenoid valves and the solenoid-operated proportional valve to provide operator-selected gear shifts in both forward and reverse directions having controlled clutch engagements achieved by modulations of clutch engagement pressure by the proportional valve. The key parameters associated with the gradual clutch engagement are all easily varied by the controller, most under program control during operation, to provide for optimized clutch engagements for smooth gearshifts. The key parameters include: fast-fill clutch delay, initial clutch engagement pressure, rate of increase of clutch engagement pressure, and the length of the reduced pressure clutch engagement interval. The electronic controller also automatically modifies selected parameters in accordance with sensed changes in temperature, magnetic flux coupling between solenoids, and variations in the voltage supply provided to the series combination of the solenoid coil of proportional valve and its solenoid driver circuit. Preferred methods of operating the electronic controller and powershift transmission are also disclosed.

This is a division of application Ser. No. 389,392, filed Aug. 3, 1989,now U.S. Pat. No. 4,967,385, which is a division of Ser. No. 055,820,filed May 29, 1987, now U.S. Pat. No. 4,855,913.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to electrical and electroniccontrol systems for transmissions in engine-driven vehicles andpower-transmitting apparatuses used in off-road vehicles, and inparticular to electronic control systems for powershift transmissions.

2. Description of the Prior Art

In the past, power transmissions have been developed in which thetransmission gear ratios are selected by electrical signals provided tosolenoid valves. In large off-road vehicles, such as agriculturaltractors, front-end loaders, road graders and the like, it is desirableto provide a large number of forward and reverse gear ratios. Due to thesize of these transmissions, and the problems of mechanically linkingoperator-actuated controls to the transmissions, it is often preferredto select transmission gear ratios entirely by the operation of solenoidvalves, as is done in a typical powershift transmission. The rate ofclutch engagement in such transmission is very dependent upon hydraulicand mechanical controls such as orifices and one or more accumulators,which in general are not very effective for providing smooth orjolt-free gear shifts under all conditions. Even when such conventionalengagement controls are set up for relatively smooth engagement of thepowershift transmission in one application, it is difficult to tailorthe clutch pressure modulation characteristics to other applications.Also, where relatively soft engagements are provided, this is oftenachieved by excessively prolonged engagement times or other undesirablecharacteristics. It may be possible to optimize a few gear shifts, forexample, of the many possible gear shifts, but the remaining gear shiftsmay be either rather too fast, and therefore rough, or too slow.

In many transmission systems, clutch pedals are provided so that theoperator may manually control the rate of clutch engagement. However, inoff-road vehicles, such as those designed for certain agricultural orconstruction equipment applications, gear shifts occur frequently, andover the course of a day represent a significant source of operatorfatigue. Also, in such manually-controlled transmissions, unnecessarytorque overloads or excessive clutch wear results whenever the operatormisjudges, or due to inexperience, inattentiveness or fatigue, is unableto provide the proper rate of clutch engagement.

The assignee of the present invention has been engaged in thedevelopment of microprocessor-based controllers for powershifttransmissions for a number of years, and has developed electroniccontrollers which electrically actuate the various solenoid-operatedhydraulic valves to select the desired transmission gear ratios inresponse to operator commands. For example, in U.S. Pat. No. 4,425,620to Bachelor et al. entitled "Electronic Control for Power ShiftTransmission," which is hereby incorporated by reference, there isdisclosed a microprocessor-based electrical control system which has amode select lever and a upshift/downshift pulser lever by which theoperator may indicate the desired vehicle direction and gear in whichthe powershift transmission is to be operated. However, this controlsystem does not provide an electronically controlled gradual engagementof the clutches of the powershift transmission during gear shifts, andsimply operates the solenoids in an on-off manner. The patent does notaddress or recognize the possibility of directly controlling ormodulating hydraulic pressures in the transmission so as to producesmooth, optimized clutch engagements during gear shifts.

The use of proportional actuator devices, such as hydraulic valvesoperated by torque motors is known in the agricultural and constructionequipment art. Such proportional actuation devices are frequentlyoperated by pulse width modulated (PWM) signals whose duty cycle isvaried in proportion to the desired average or DC value desired to beproduced by the actuator means. However, as far as we are presentlyaware, such proportional actuation devices have not been used onpowershift transmissions before the present invention. This may in bedue in part to the inherent problem associated with using suchrelatively delicate or sensitive equipment which must be finelycontrolled in the rugged and environmentally severe conditions to whicha typical powershift transmission in an off-road vehicle is exposed. Inthe development of the present invention, applicants encountered anumber of unexpected problems which had to be overcome to successfullyapply the concept of utilizing a PWM solenoid valve as a proportionalactuator device in a powershift transmission to obtain the controlledclutch engagements necessary to achieve smooth gear shifts under a widevariety of operating conditions.

Accordingly, a primary object of the present invention is to provide aelectronic control system for a powershift transmission which utilizes aproportional actuation means, such as a proportional hydraulic valveoperated by a solenoid supplied with an alternating electrical signal,such as a PWM signal, to automatically control the hydraulic system ofthe transmission to provide gradual clutch engagements required forsmooth, efficient gear shifts.

Another important object of the invention is to provide an electroniccontrol system which allows a number of key parameters to be quicklyadjusted and stored in the memory of microprocessor means, so that theoperation of proportional actuation devices associated with hydraulicvalves within a powershift transmission can be readily tailored to fitalmost any vehicle application to provide for quick and smooth clutchengagements.

Yet another object is to provide an electronic control system which cancustomize the clutch engagements in a powershift transmission forvirtually all gear shifts.

Still another object of the present invention is to provide a controlsystem which automatically compensates for a number of variables whichwould otherwise detrimentally influence the quality of clutchengagements in a powershift transmission, including changes intemperature of the transmission and solenoids and in the magneticcoupling between adjacent solenoid coils of the solenoid-operatedhydraulic valves.

One more object of the present invention is to eliminate the need toprovide a separate voltage regulation supply to feed electrical power toa proportional solenoid used in an off-road vehicle, by providing forautomatic adjustment of the duty cycle of the PWM signal driving theproportional solenoid which counteracts changes in or drifting of thenominal voltage in the vehicle's electrical supply system.

SUMMARY OF THE INVENTION

In light of the foregoing problems and objects, there is provided,according to one aspect of the present invention, an electronic improvedcontrol system for a powershift transmission having a plurality ofhydraulically-actuated clutches and a plurality of electrically-operatedhydraulic valves for selecting the clutches for engagement, each suchvalve being provided with electrical coil means for operating the valve.The control system comprises: first electrical switching means forproviding a first electrical signal to a first electrical coil meansassociated with a first hydraulic valve for selecting a first clutch ofthe transmission for engagement; second electrical switching means forproviding a second electrical signal which is a proportional signal to asecond electrical coil means associated with a second hydraulic valvefor adjusting the hydraulic pressure applied to the first clutch duringthe engagement thereof; microprocessor means for operating the powershift transmission in accordance with operating parameters stored withinthe microprocessor means, the operating parameters including a firstparameter corresponding to a reduced hydraulic pressure to be applied tothe first clutch during the initial engagement thereof. Themicroprocessor means includes first output means for controlling thefirst electrical switching means, and second output means forcontrolling the second electrical switching means. It also includesmeans for causing the second electrical signal to command the secondhydraulic valve to adjust the hydraulic pressure applied during initialengagement of the clutch in accordance with a stored value of the firstparameter. The second electrical signal is preferably a pulse widthmodulated (PWM) signal. The first and second electrical coil means arepreferably solenoid coils, and the first and second electrical switchingmeans may be and preferably are substantially identical in construction.The operating parameters stored within the microprocessor preferablyalso include a second parameter corresponding to the maximum length oftime reduced hydraulic pressures to be applied to the first clutchduring engagement thereof, and a third stored parameter corresponding tothe rate at which hydraulic pressure applied to the first clutch duringengagement thereof is to be increased from the reduced pressure appliedduring the initial engagement of the first clutch. A third storedparameter may also be provided for providing a predetermined time delaybetween the application of the first electrical signal to the firstelectrical coil means and the application of the second electricalsignal to the second electrical coil means. This time delay allows theclutch pack of the clutch to be engaged to fill with hydraulic fluid ata high flow rate caused by normal hydraulic pressure, which is thenreduced in value at the point where the clutch pack is filled and theclutch begins to engage.

According to a second aspect of the invention there is provided anelectronic control system for a powershift transmission that has aplurality of gears having different gear ratios and a plurality ofhydraulically-actuated clutches for engaging and disengaging the gearsby locking and unlocking the gears to shafts within the transmission.The transmission also includes the electrically-operated hydraulicvalves and electrical coil means for operating each valve describedaccording to the first aspect of the present invention. The controlsystem of the second aspect comprises: first electrical switching meansfor providing a first electrical signal to a first electrical coil meansassociated with the first hydraulic valve for selecting a first clutchof the transmission for engagement; second electrical means forproviding a second electrical signal to a second electrical coil meansassociated with a second hydraulic valve for selecting a second clutchof the transmission for engagement; third electrical switching means forproviding a third electrical signal which is a proportional signal to athird electrical coil means associated with a third hydraulic valve foradjusting the hydraulic pressure applied during the engagement of thefirst clutch and during the engagement of the second clutch. The controlsystem further comprises microprocessor means for operating thepowershift transmission in accordance with operating parameters storedwithin the microprocessor means, said operating parameters includingfirst and second stored values of a first parameter corresponding to adesired characteristic of hydraulic operation to be achieved duringengagement of the first clutch and during engagement of the secondclutch, the first and second values being distinct from one another. Themicroprocessor means also includes first output means for controllingthe first electrical switching means, second output means forcontrolling the second electrical switching means, third output meansfor controlling the third electrical switching means, and means forcausing the third electrical signal to command the third hydraulic valveto adjust the hydraulic pressure applied during engagement of the firstand second clutches respectively in accordance with the first and secondvalues of the first stored parameter.

According to a third aspect of the present invention, there is providedan electronic control system for compensating for the effectivetemperature changes in a powershift transmission having at least oneelectrically-operated proportional hydraulic valve means for adjustingat least one parameter within the transmission. The electronic controlsystem comprises: first electronic switching means for providing to thesolenoid coil a first electrical signal which is an alternatingelectrical signal corresponding to a desired value of the parameter;means for sensing the value of a second parameter indicative of theapproximate temperature of the transmission; means for determining thedifference between an expected value of the second parameter at apredetermined temperature of the transmission, and the sensed value ofthe second parameter; and means for adjusting the first electricalsignal in response to the determined difference to compensate for theeffective temperature changes in the transmission. In this controlsystem the first electrical signal is preferably a pulse width modulated(PWM) signal.

According to a fourth aspect of the present invention, there is providedan electronic control system for compensating for the effect of magneticcoupling between at least two solenoid coils in a powershifttransmission having a plurality of hydraulically-actuated clutches andplurality of electrically-operated hydraulic valve means for selectingthe clutches. Each such valve clutch means includes a solenoid coil tooperate the valve. The electronic control system comprises: firstelectrical switching means for providing to a first one of the solenoidcoils associated with a hydraulic valve which is a proportionalmodulation device a first electrical signal; second electrical switchingmeans for providing to a second one of the solenoid coils locatedadjacent to the first solenoid coils, a second electrical signal,whereby magnetic flux is produced by the second one of the solenoidcoils which affects by magnetic coupling the intended operation of thefirst coil; means for determining whether such magnetic coupling ispresent; and means for compensating for the effect of such magneticcoupling between the second and first ones of the solenoid coils byadjusting the first signal so as to counteract the effect of such fluxcoupling.

According to a fifth aspect of the present invention, there is providedan improved electronic control system for use with a powershifttransmission. The electronic control system is of the type whichincludes electronic switching means connectable in series with asolenoid coil of a hydraulic valve means used to adjust at least oneparameter within the transmission. The electronic switching means andsolenoid coil form a series combination to which a DC supply voltage isapplied across. The improvement in the electronic control systemcomprises in combination: sensing means for determining the actual valueof the supply voltage provided across the series combination of thesolenoid coil and the electronic switching means; means for determiningthe difference between the actual value of the supply voltage and apredetermined nominal voltage value of the supply voltage; andcompensation means for adjusting the second signal in inverse proportionto the value of the difference, thereby compensating for variation inthe supply voltage.

According to a seventh aspect of the present invention, an electroniccontrol system for compensating for the effect of temperature changes inthe transmission, for the effect of magnetic coupling between solenoids,and for variations in the supply voltage, is provided by combining thevarious features of the third, fourth and fifth aspects of the presentinvention.

Although the foregoing aspects of the present invention have beendeveloped for use in conjunction with a powershift transmission, werecognize the applicability of a number of the foregoing aspects of thepresent invention to power-transmitting apparatuses, particularly thosefor use in or with an off-road vehicle, which have solenoid-operatedhydraulic valves as actuator means.

In all of the foregoing aspects of the present invention, it ispreferred to provide microprocessor means, including memory means forprogram storage for operating the power-transmitting apparatus inaccordance with operating parameters stored in the memory means. In eachaspect of the present invention, at least one of the stored operatingparameters preferably represents a value corresponding to either aproportional alternating signal such as a PWM signal, or the magnitudeof an adjustment made in response to a sensed condition, such astemperature, flux coupling between solenoids, or voltage variation.

While the foregoing aspects of the present invention have been describedin terms of electronic control systems for accomplishing various tasks,we believe that the methods employed by or implemented with the controlsystems of the present invention represent novel approaches to theproblems addressed by and solved by the present invention, and thusthese methods constitute part of our invention.

These and other aspects, objects, features and advantages of the presentinvention will be more fully understood from the following detaileddescription and appended claims, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, where identical reference numerals orreference characters represent like items shown in the various Figures:

FIG. 1 is a block diagram illustrating the transmission control systemof the present invention;

FIG. 2 is a side elevational view shown in partial cross-section of apowershift transmission controlled by the electronic control system ofthe present invention;

FIG. 3 is a cross-sectional view of a shaft used in one of the twostages of the FIG. 2 transmission;

FIG. 4 is a front view schematic diagram of the head set gears of theFIG. 2 transmission;

FIG. 5 is a hydraulic diagram for the FIG. 2 transmission;

FIG. 6 is a table showing the solenoids which must be energized toselect the various forward and reverse gears in the FIG. 2 transmission;

FIG. 7 is a simplified plan view of the hydraulic valve manifold withthe six solenoid-operated valves shown disposed adjacent one another;

FIG. 8 is a detailed block diagram showing the components of the FIG. 1electronic control system, including circuit details of the outputsection providing electrical signals to the transmission solenoids;

FIG. 9 is schematic diagram showing five proximity switches whichprovide input signals to the FIG. 8 electronic control system;

FIG. 10 is a schematic diagram of opto-isolator input circuits for twoinput signals for the FIG. 8 control system;

FIG. 11 is a fragmentary side view in partial cross-section of a clutchpedal assembly which may be used with the FIG. 1 control system;

FIG. 12 is a schematic diagram of a circuit for providing power to theFIG. 8 control system;

FIG. 13 is a detailed schematic diagram of two transmission solenoiddriver circuits used in the FIG. 8 control system;

FIG. 14 is a generalized flowchart showing the overall organization ofthe software used with the electronic system of the present invention;

FIG. 15 is a graph showing the duty cycle of the electrical signalsupplied to the pulse width modulation solenoid during engagement of atypical hydraulically-actuated clutch in the FIG. 2 transmission, suchelectrical signal being produced by the FIG. 1 control system;

FIG. 16 is a detailed flowchart showing the general sequence followed bythe software to produce the electrical signal shown in FIG. 15;

FIG. 17 is an alternate duty cycle versus time graph for the electricalsignal applied to the pulse width modulation solenoid during engagementof a hydraulically-actuated clutch in the FIG. 2 transmission;

FIG. 18 is a table listing gear shifts which can be provided by the FIG.1 control system, and illustrating that different values of fourdifferent parameters may be set for each individual gear shift; and

FIGS. 19-21 are graphs showing hydraulic clutch pressure, vehicle outputspeed, and transmission output torque as a function of time illustratingthe effect of the various FIG. 18 parameters, with FIG. 19 illustratingthe effect of a substantially constant, reduced clutch pressure duringclutch engagement, FIG. 20 showing the effect of introducing a delay inthe reduction of substantially constant clutch pressure during clutchengagement, and FIG. 21 showing the effect of a constantly increasingclutch pressure in addition to the time delay illustrated by FIG. 21.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The Vehicle DriveSystem (FIG. 1)

A drive system for an off-road vehicle which utilizes the transmissioncontrol system of the present invention is illustrated in FIG. 1. Thevehicle's drive system includes internal combustion engine 14 whichsupplies the power to output drive shaft 16 through a drive trainincluding input drive shaft 18 and transmission 20. In the preferredembodiments of the present invention, the transmission 20 is of the typewhich has a plurality of gear ratios which are selected by actuation ofselected solenoid valves. A total of four forward gears and four reversegears are provided. Transmission 20 has six clutches as shown in Table1:

                  TABLE 1                                                         ______________________________________                                        Clutch Name        Clutch I.D.                                                ______________________________________                                        forward directional clutch                                                                       FDC                                                        reverse directional clutch                                                                       RDC                                                        first gear speed clutch                                                                          1SC                                                        second gear speed clutch                                                                         2SC                                                        third gear speed clutch                                                                          3SC                                                        fourth gear speed clutch                                                                         4SC                                                        ______________________________________                                    

In order to engage any forward gear or any reverse gear, two clutchesmust be engaged, namely the appropriate directional clutch and theappropriate speed gear clutch. For example, to place the transmission 20into the third forward gear, both the forward directional clutch andthird gear speed clutch must be engaged. Engaging speed clutch withoutalso engaging one of the directional clutches effectively results in thetransmission being in neutral, since the input shaft and the outputshaft of the transmission will not be coupled together.

In this preferred embodiment of the present invention, there are a totalof six solenoid valves 22a-22f, one or two of which must be actuated atany one time to select a particular gear ratio. Electrical power to allof the solenoid valves is provided from vehicle electrical supply line23, having a direct current (DC) supply voltage V_(B) such asapproximately +12 volts supplied from the vehicle's normal electricalpower supply system (not shown), through the vehicle's OFF-ON-IGN switch24, and a normally closed switch 25 located on the manual clutchengagement control 26. The electrical power for the solenoids whichcause the engagement of the directional clutches is further routedthrough a switch 27 on a parking brake control 29 actuated by applyingparking brake lever 31, and a neutral safety start switch 28, connectedas shown. Electronic controller 30 selects the gear ratio oftransmission 20 by selectively providing a ground connection throughsolenoid control lines 32a-32f to solenoids of solenoid-operated valves22a-22f. The function of each valve 22 is listed in Table 2, along withthe mnemonic used to identify its respective solenoid.

                  TABLE 2                                                         ______________________________________                                        Valve  Solenoid   Function of Valve When Its                                  Ref. No.                                                                             Ref. Symbol                                                                              Solenoid Is Energized                                       ______________________________________                                        22a    1SS        engages first speed clutch 1SC                              22b    2SS        engages second speed clutch 2SC                             22c    3SS        engages third speed clutch 3SC                              22d    FCS        engages forward dir. clutch FDC                             22e    RCS        engages reverse dir. clutch RDC                             22f    PMS        provides proportional modulation of                                           hydraulic pressure during engage-                                             ment of clutches FDC and RDC                                ______________________________________                                    

The configuration and operation of valves 22, their solenoids and theelectrical circuits driving solenoid control lines 32 will be fullyexplained later.

The driver or operator of the vehicle provides input signals tocontroller 30 by means of mode select control 34, upshift/downshiftcontrol 36 and an optional manual clutch engagement control 26. Modeselect control 34 has a three-position, detented mode select lever 35movable between a center neutral (N or NEUT) position, a reverse (R orREV) position, and a forward (F or FWD) position. Electrical signals aresupplied from mode select control lever 35 to controller 30 which causescontroller 30 to select the proper operating mode. Mode select lever 35also controls neutral safety start switch 28. When mode select lever 35is in the N position, it causes neutral start switch 28 to disconnectpower from the solenoid valves 22 which select the forward directionalclutch or reverse directional clutch for engagement. At the same time,neutral start switch 28 provides electrical power to starter circuitry(not shown) for starting engine 14. Mode select lever 35 and startswitch 28, therefore ensure the transmission is in neutral whenever thelever is in the neutral position, regardless of the state of solenoidcontrol lines 32.

Upshift/downshift control 36 has a three-position,spring-returned-to-center pulser lever 37 which provide upshift pulses(UP) and downshift pulses (DN) to controller 30. In its center or normalposition, pulser lever 37 does not produce upshift or downshift pulses.When lever 37 is moved forward into its UP position, an upshift pulse isprovided. If the driver maintains lever 37 in the upshift position, noadditional pulses are produced. To obtain further upshifts, the levermust be returned to its UP position and then to its forward position.Similarly, movement of pulser lever 37 in a rearward direction to its DNposition produces one downshift pulse. To obtain another downshift pulsethe lever 37 must be returned to neutral and then into its DN position.(If desired, the holding of the lever 37 in either the UP position or DNposition could alternatively provide further upshift pulses or downshiftpulses respectively at predetermined time intervals until lever 37 isreturned to its normal position.) The upshift and downshift pulses fromcontrol 36 are used by controller 30 to upshift or downshifttransmission 20. These upshifts and downshifts can occur when modeselect lever 35 is in either the forward position or the reverseposition, and also preferably can occur when lever 35 is in its neutralposition. Suitable mechanical constructions for the mode control 34 andthe pulser control 36 are shown in detail in the aforementioned U.S.Pat. No. 4,425,620, with the various needed proximity sensor andmicroswitches required to produce electrical pulses mounted thereon.

Throttle control 38 has a throttle lever 39 which is mechanically orotherwise linked in conventional manner to engine 14 to control thespeed of engine 14. Manual clutch engagement control 26 includes apivotable lever such as spring-returned clutch foot pedal 42, whoseposition is monitored by clutch pedal potentiometer 44 and proximitysensor or switch 46. The sensor 46 detects the presence of the clutchpedal 42 at the top of its travel, when the pedal is not depressed atall. An analog signal on line 45 is provided to the controller 30 bypotentiometer 44. A digital signal is provided on line 47 by the sensor46 to electronic controller 30 to indicate the sensed position of pedal42.

The manual clutch engagement control 26 is optional. It provides a meansfor the operator to manually control the clutch engagements in a mannersimilar to that in a conventional vehicle wherein the clutch pedal ismechanically linked to the transmission. Control 26 permits the operatorto feather the clutch and to disengage the engine from the transmissionand drive shaft. Sensor 46 senses whenever the clutch pedal 42 isdepressed from its normal top position, and begins to feather the clutchby reducing the hydraulic pressure applied to the currently selecteddirectional clutch. The reduction in hydraulic pressure is proportionalto the relative position of the clutch pedal 42 as sensed by clutchpotentiometer 44 and reflected in the analog value of signal 45. Inaddition, whenever the clutch pedal 42 is fully depressed, it actuatesnormally closed switch 26 located very near the end of the bottom oftravel of the pedal 42, thus breaking the supply of power from the +12volt supply line 23 to solenoid valves 22a-22f. One benefit of themanual clutch engagement control 26 is that the driver of a vehicle (forexample, an agricultural tractor pulling a ground-engaging draftimplement) in the field and is pulling a plow or can, upon observing anobstacle, stop his vehicle and then proceed to inch around the obstacleat a very slow rate of speed in the first forward gear (or first reversegear) by use of the clutch pedal 42.

In the preferred embodiments of the present invention, the controller 30also supplies output signals to a display 50, which may be a multiplecharacter liquid crystal display (LCD). Display 50 may be used toprovide visual information to the operator, such as the present gearselected by the controller 30, the mode (forward, neutral or reverse)selected by the operator, or other information as will be laterexplained. In the absence of more urgent information, the display 50always indicates to the driver the speed gear which is currently engagedwithin transmission 20, and the directional gear (if any) which iscurrently engaged.

The operation of the drive system of FIG. 1 from an operator's isviewpoint is generally as follows. The engine 14 is started when modeselect lever 35 in its neutral (N) position. Neutral safety start switch28 disconnects power to the directional solenoid valves 22 and providespower to the starter circuit. Transmission 20, therefore, is in neutral.Assuming the driver has not yet moved the pulser lever 37, thecontroller 30 will default to first gear as the selected gear, andengage the first speed gear clutch. As previously explained, engaging aspeed gear clutch without engaging a directional clutch does not takethe transmission out of neutral.

When the driver moves the mode select lever 35 from N to F, controller30 actuates the appropriate solenoid valve 22 to engage the forwarddirectional clutch to place transmission 20 into the first forward gear.As will be explained, the controller 30 automatically provides for acontrolled gradual engagement of the selected directional clutch for thesmooth shifting from neutral to first gear without lurching or otherobjectionable shocks or torque spikes being present. If desired, theoperator can use clutch pedal 42 to manually modulate the transmission20, so as to feather the drive. However, this is not necessary unless aslower than normal clutch engagement for the gear which has beenselected is desired.

Gears higher than the first forward gear are obtained by moving thepulser lever 37 to its UP position. One movement of the pulser lever 37to up-shift position provides a single upshift pulse. Pulsing the pulserlever 37 rearward to its DN position gives the reverse effect. Eachdownshift pulse provided to controller 30 causes the controller tochange the particular solenoid valves which are actuated to produce thedesired downshifting of the transmission 20. Controller 30 does notpermit downshifting from first forward gear to either neutral or reverseby means of the pulser lever 37. Similarly, it does not permit shiftingfrom first (or any other) reverse gear to neutral or a forward gear bymeans of pulser lever 37. Such shifts can be achieved only by use of themode select lever 35.

When the mode lever 35 has been in its N position and then is placed inthe R position, controller 30 actuates the proper solenoids 22a-22f toprovide first reverse gear. Higher reverse gears, that is reverse gearswith a higher gear ratio than the first reverse gear, are normallyobtained by pulsing lever 37 from its normal position to its UPposition, as is done in the forward mode.

If desired, controller 30 may be programmed so as to allow gears abovethe first forward gear or below the first reverse gear to be modulatedby the clutch pedal 42. However, for the preferred embodiment oftransmission 20, it is presently preferred to only allow first gearforward or reverse to be so modulated. Depressing clutch pedal 42 causesclutch position sensor 46 to provide a signal to controller 30. In thepreferred embodiment, if the transmission 20 is not in first forward orreverse gear, controller 30 preferably immediately deenergizes allsolenoid valves 22a-22f, to cause transmission 20 to be shifted toneutral.

In the preferred embodiment, the electronic controller 30 allows thetransmission 20 to be shifted from neutral to any gear previouslyselected by use of the pulser lever 37. For example, if the operatorwishes to go from neutral to second gear, he need only actuate thepulser lever 37 until display 50 indicates that the second speed gearhas been selected. Then, he may shift the mode lever 35 from N to eitherF or R to put the transmission 20 into the second forward gear or secondreverse gear respectively. This gear-skipping feature, which may bereferred to as skip-shifting, allows the operator of a lightly loadedvehicle to avoid unnecessary upshifting or downshifting to placetransmission 20 into any gear he desires from neutral. As will be laterexplained in detail, the electronic controller 30 provides foradjustment of hydraulic parameters which, for a lightly loaded vehicle,will permit transmission 20 to shift smoothly from neutral to a highergear in either forward or reverse.

A feature related to skip-shifting is shuttle-shifting, which is thedeliberate shifting by the operator from a current higher forward gearto a pre-selected higher reverse gear, and vice-versa, without requiringthe operator to manually place the transmission in neutral. Thus, if anoperator on a front-end loader wishes to go directly from second gearreverse to second gear forward, and back again (such as might be donerepetitively when performing a repetitive loading operation), theelectronic controller 30 can readily be arranged to allow such directshifting. In a preferred embodiment of the present invention, toshuttle-shift the operator need not touch the pulser lever 37, but onlyneed move the mode lever 35 from F to R (or vice versa). Controller 30does not expressly recognize the intent of the operator to perform ashuttle shift. However, when the operator shifts the mode lever 35 fromF to R (or vice versa) without upshifting or downshifting while lever 35is in its N position, controller 30 selects the speed gear to be engagedaccording to the shuttle-shift combination associated with the mostrecently engaged gear of the opposite direction.

Transmission 20 (FIGS. 2 through 4)

FIG. 2 is a detailed side elevational view of a preferred embodiment oftransmission 20 of FIG. 1 selectively cut away in partial cross-sectionto better show its internal construction. Also, for illustrationpurposes, the first and second stages of transmission 20 are shownarranged vertically to one another, when in fact, they are actually atthe same horizontal elevation within transmission 20. This embodiment oftransmission 20 was very recently developed by the Funk ManufacturingDivision of Cooper Industries, Inc. in Coffeyville, Kans. The particulartransmission described is known as the Funk 5000 Series transmission.The mechanical, hydraulic and operational features of a Funk 5000 Seriestransmission are described in detail in J. Goodbar and M. Testerman,"The Design and Development of a Four Speed Powershift Transmission WithElectronic Clutch Pressure Modulation," SAE Technical Paper No. 861212.Proceedings of the Off-Highway and Power Plant Congress and Exposition,held in Milwaukee, Wis. on Sept. 8-11, 1986, which is herebyincorporated by reference. Among other things, this technical paperdescribes a number of the advantages achieved by using a pulsewidth-modulated solenoid-operated proportional valve achieve hydraulicpressure modulation and torque load characteristics which are tailorableto specific vehicle application requirements so as to provide relativelysoft, optimized engagements of forward and reverse direction clutches.We developed the electronic control system of the present inventionunder the auspices of the assignee of the present invention in part toelectronically control and operate the Funk 5000 Series transmission. Inso doing we provided the electronic means by which the shifting andperformance of Funk's new transmission could be controlled and optimizedin all gears and environmental conditions.

The transmission 20 features a gear train, which includes first andsecond stages 62 and 64 having three clutches each, interconnecting aninput shaft 66 and output shaft 68 through these clutches and variousgears which will shortly be described. The shafts, gears and othercomponents of the transmission are mounted to and enclosed within asuitably sturdy housing assembly 69 provided with various removablehousings such as the main or rear housing 70 and front cover housing 71.The input shaft 66 is connected to the impeller 75 of an SAE torqueconverter 72 located within bell housing 73. The turbine 74 is connectedto the driven turbine shaft 76 of converter 72 upon which is rigidlypositioned a turbine gear 78, that serves as the input gear for the mainportion of transmission 20. An idler gear 82 rotatably mounted on shaft84 is positioned between turbine gear 78 and forward and reverse hubgears 86 and 88. The three clutches of the first stage 62 consist offorward directional clutch FDC and first and third speed clutches 1SCand 3SC. Clutch packs 92, 94 and 96 respectively are found therein. Thethree clutches of the second stage 64 consist of reverse directionalclutch RDC and second and fourth speed clutches 2SC and 4SC, which haveclutch packs 102, 104 and 106 respectively located therein. In FIGS. 2and 3, the clutch packs are shown in schematic form to avoidunnecessarily cluttering the Figures. The gear ratios for both theforward and reverse directions are identical, namely: 4.167; 2.285;1.178; and 0.589.

Identical clutch hubs 110 are welded to the first, second, third andfourth range hub gears 111, 112, 113, and 114. The clutch hubs 116 and118 of the forward and reverse hub gears 86 and 88 are identical to oneanother and longer than the speed clutch hubs 110. First and secondstage cylinder gears 124 and 126 are also identical. The forward hubgear 86 is identical to the reverse hub gear 88. Identical cylinders areused on the speed clutches 1SC, 2SC, 3SC and 4SC. The cylinders on thedirectional clutches FDC and RDC are also identical to one another.

The speed clutch cylinders 127 and 128 are welded to center support webssuch as webs 129 and 130 that are welded to the main shafts 132 and 134of first and second stages 62 and 64 respectively. FIG. 3 show across-sectional view of one of the stage shafts and its associatedclutches, namely shaft 132 of the first stage 62, to illustrate thesedetails more clearly. The center support webs such as web 127 supportsthe integral cylinder gears as well as providing the sealing surfacebore for the outer seal on the clutch apply pistons such as pistons 133and 135. The directional clutch cylinders are removable and mount onsplines that have been machined on the main shafts 132 and 134. When theinternal splines are broached on the cylinders, one tooth is removedevery 60°. This space is utilized to drill holes to allow cooling fluidto exit from the clutch packs and return to the transmission sump.

As shown best in FIG. 3, gun-drilled axial hole 137 provides coolingfluid to the clutch packs and various bearings used within thetransmission 20. The other gun-drilled holes 138, 139 and 140 which aregun-drilled parallel and to spaced from the hole 134 supply pressurizedcharge fluid to the three hydraulically actuated clutches FDC, ISC and3SC mounted on the shaft 132. As best shown in FIG. 3, clutch pistonreturn springs, such as belleville-type springs 142 and 144 respectivelyassociated with the forward directional clutch 92 and the third speedclutch 96, are provided to return the apply pistons of these clutches totheir disengaged state in the absence of sufficient hydraulic pressurebearing against the apply pistons to overcome the springs.

As illustrated in FIG. 2, on output shaft 68 of transmission 20 arekeyed or pinned a first and second range output gear 162 and a third andfourth range output gear 164. Output gear 162 is meshingly engaged bysecond range hub gear 112 rotatably mounted upon second stage shaft 134.Hub gear 112 is one-half of a compound gear 166, the other half beinggear 168, which meshes with first range hub gear 111. The third andfourth range output gear 164 is engaged by fourth range hub gear 114rotatably mounted upon second stage shaft 134. Gear 114 is, in turn,meshingly engaged by third range hub gear 113 rotatably mounted uponfirst stage shaft 132.

First and second stages 62 and 64 of transmission 20 are each providedwith rotary hydraulic couplings 168 and 170 to enable hydraulicconnections to be made to rotating shafts 132 and 134. Transmission 20includes an auxiliary power take-off (PTO) unit 182 and transmissioncharge pump 164 coupled to turbine shaft 76 of torque converter 72. Thehydraulic pump 184 obtains hydraulic fluid from the bottom of the mainhousing 70 through a removable tubular suction screen or strainer 186that connected by suction line 188 to the pump inlet 190. As may beappreciated from the radially-arranged holes 194 connected to axial hole137 in shaft 132 as shown in FIG. 3, the hydraulic pump 184 providescooling fluid which flows through the clutch packs and lubricates thebearings. The pressurized transmission oil is also used to operate thesix clutches of transmission 20 in a manner which will shortly befurther explained.

The operation of the gear train of transmission 20 may be understoodwith the aid of the simplified headset gear diagram shown in FIG. 4.When turbine gear 78 rotates in a clockwise direction as shown by arrow176, idler gear 84 rotates in a counterclockwise direction as shown byarrow 177, causing forward and reverse hub gears 86 and 88 to rotate ina clockwise direction as shown by arrows 178 and 179. When any forwardgear is desired, forward directional clutch FDC is engaged by supplyinghydraulic fluid through gun-drilled hole 138 leading to its clutch pack92, causing the clutch apply piston therein to move and forcing theclutch plates of the clutch pack to frictionally engage. In the firstforward gear, first cylinder gear 111 is caused to rotate in a clockwisedirection by the engagement of its clutch pack 94, which in turn causessecond range hub gear to rotate in free-wheel fashion in acounterclockwise direction, and output gear 162 to rotate in clockwisedirection, thus turning output shaft 68 clockwise. In second forwardgear, first cylinder gear 124 rotates in clockwise direction, causingsecond cylinder gear 126 to rotate in a counterclockwise direction.Second gear speed clutch 2SC is engaged, which causes second cylindergear 126 and second range hub gear 112 connected thereto to rotate in acounterclockwise direction, thus rotating output gear 162 and outputshaft 86 in a clockwise direction. To engage the third forward gear, thethird gear speed clutch 3SC is engaged, causing third range hub gear 113to rotate in a clockwise direction, which causes fourth range hub gear114 to freewheel in a counterclockwise direction on shaft 134, androtate output gear 164 and output shaft 68 in a clockwise direction. Toengage fourth forward gear, fourth speed gear clutch 4SC is applied,locking fourth cylinder gear 114 to cylinder gear 126 which is rotatingin counterclockwise direction on account of its meshing engagement withfirst stage cylinder gear 124, causing fourth range hub gear 114 todrive output gear 164 and output shaft 68 in a clockwise direction.

The operation of the four reverse gears may be readily explained in asimilar manner that should be obvious to those skilled in the art frominspection of FIG. 2. Briefly, when in the reverse mode, the reversedirectional clutch RDC is engaged, locking the reverse clutch hub 118and reverse hub gear 82 to second stage shaft 134 so that it is poweredby idler gear 84 and running in a clockwise direction. In second andfourth reverse gears, power is provided directly from shaft 134 to theoutput gear 162 or 164 on output shaft 168 by respective engagement ofsecond speed gear clutch 2SC or fourth speed gear clutch 4SC. Cylindergear 126 welded to shaft 134 causes the cylinder gear 124 welded toshaft 132 of first stage 62 to rotate in a counterclockwise direction.This enables first and third speed gear clutches 1SC and 3SC whenengaged to cause their respective hub gears 111 and 113 to rotate in acounterclockwise direction and to transmit power through thenfree-wheeling hub gears 112 and 114 on the second stage shaft 134 to theoutput gears 162 and 164 of output shaft 68.

Hydraulic System (FIGS. 5 through 7)

FIGS. 5 through 7 relate to the hydraulic system 210 used to control theengagement and lock-up of the clutches of transmission 20. The hydraulicsystem 20 is shown with conventional hydraulic symbols in schematic formin FIG. 5. The hydraulic power supply section 212 of the hydraulicsystem 210 includes: a hydraulic reservoir or sump 214 (which is thebottom interior chamber of the transmission housing assembly 69 shown inFIG. 2); the strainer 186; the hydraulic pump 184; a high pressurefilter assembly 215 with a ten micron filter 216 having a spring-loadedbypass check valve 218 provided with an electrical switch 220 toindicate when filter 216 is being bypassed; and a main or systempressure relief valve 222. The relief valve 22 is the main pressureregulator for the hydraulic system and is connected to high-pressureoutput conduit or hydraulic line 224. The power supply 212 also includesa second pressure relief valve 226 to ensure that the back-pressure ofthe hydraulic oil dumped over main relief valve 222 into discharge line227 does not overpressurize the torque converter 72. The discharge flowfrom relief valve 222 enters the torque converter 72 and is then passedthrough a transmission heat exchanger 230. This cooled flow is thendirected to the transmission bearings and clutch packs via hydraulicfeed lines 232, 234 and 236. Line 234 feeds the axial hole 137 via therotary coupling 168 on shaft 132 of first stage 62, while the line 236feeds a similar axial hole via the rotary coupling 170 on shaft 134 ofoutput stage 64.

The high-pressure fluid in main line 224 from the hydraulic power supply212 is routed to the directional clutches FDC and RDC through a clutchpressure modulation circuit 238 within the dot-dash line which includesa pressure reducing valve 240 which acts as a second hydraulic pressureregulator. The pressurized fluid from line 224 is also directed to thespeed clutch valves 22a-22c via feed line 242 without first passingthrough the reducing valve 240. The purpose for this particular routingof pressurized hydraulic fluid is to allow the speed clutches 1SC-4SC toengage and synchronize before modulation and synchronization of thedirectional clutches FDC and RDC occur. In other words, the intent ishave the major portion of the clutch energy be absorbed by thedirectional clutches and not the speed clutches during any clutchengagement.

Also, the hydraulic valve circuit 246 (surrounded by dashed lines) isarranged to prevent any two of the speed clutches or any two of thedirectional clutches from being engaged at the same time. This isachieved by a series path design for both the directional and speedclutch fluid supply circuit.

The hydraulic valve circuit 246 includes the six solenoid-operatedhydraulic valves 22a through 22f. Each of these solenoid-operated valvesis a conventional, single-solenoid, two-position, spring-returned valve.Valves 22a through 22e are shown as four-way valves intended for on-offor "bang-bang" operation, while valve 22f is a two-way valve intendedfor operation as a proportional value having an adjustable orificebetween its inlet port and output port. When solenoid 1SS of valve 22ais energized, it shifts the valve spool within valve 22a, causinghydraulic line 242 to be placed in fluid communication with line 252,thereby providing hydraulic fluid to the first speed clutch 1SC locatedon stage 62. When solenoid 3SS of valve 22c is energized pressurizedhydraulic fluid in line 254 is directed to line 256, which in fluidcommunication with the third speed clutch 3SC located on the first stage62. Note that solenoid 1SS must be deenergized in order for the thirdspeed clutch 3SC to be actuated. When solenoids 1SS, 2SS and 3SS aredeenergized, pressurized fluid flowing serially through lines 242, 254and 258 is supplied to line 260 which is in fluid communication with thefourth speed clutch 4SC located on the second stage 64. If solenoid 2SSis thereafter energized, the pressurized fluid from line 258 is directedtoward line 262 for delivery to and actuation of the second speed clutch2SC.

Hydraulic fluid to engage the forward directional clutch FDC and thereverse directional clutch RDC is provided from main line 224 throughpressure regulator 240. When solenoid FCS of valve 22d is deenergized,the hydraulic fluid in line 272 downstream from regulator 240 is routedto hydraulic feed line 274, which leads to valve 22e. If solenoid RCS ofvalve 222 is deenergized, the fluid in line 274 is blocked by pluggedport 275 of valve 223 and does not pressurize or flow to the reversedirectional clutch RDC. When solenoid RCS of valve 22e is energized,thereby shifting the valve spool of valve 22e, pressurized fluid fromline 274 is directed to line 276, which is in fluid communication withthe reverse directional clutch RDC, thereby applying clutch RDC. Whensolenoid FCS of valve 22d is energized, valve 22d actuates, connectingline 274 to the tank, that is, to the reservoir or sump 214 throughdrain line 277, thus completely depressurizing line 274. Thus, thereverse directional clutch RDC is disengaged, even if solenoid RCS werestill energized (which it should not be). Energizing solenoid FCS alsocauses valve 22d to direct the pressurized fluid in line 272 to line 278in fluid communication with the forward directional clutch FDC, thusapplying clutch FDC.

Each of the solenoid-operated valves 22a-22f has a drain line like drainline 277. Each of the six clutches in transmission 20 is in fluidcommunication through one of these drain lines with the sump 214whenever not selected for engagement by energization and actuation ofthe appropriate solenoid and its associated valve 22. This hydraulicdesign results in the clutches quickly disengaging whenever they are nolonger selected for actuation. Note that when none of the first threespeed clutches 1SC, 2SC and 3SC are selected for actuation byenergization of solenoids 1SS, 2SS or 3SS, then, by default, the fourthspeed clutch is automatically selected by the hydraulic valve circuit246 for engagement.

FIG. 6 is a truth table which shows which solenoid or solenoid pair mustbe energized in order to put the transmission 20 into the first reversegear (REV1) through fourth reverse gear (REV4), and into the firstforward gear (FWD1) through fourth forward gear (FWD4). As can bedetermined by studying FIGS. 2 and 5, gears 1 through 3 can only beobtained by energizing two solenoids, namely the appropriate speedsolenoid and the desired directional solenoid. Gear REV4 can be obtainedby energizing only solenoid RCS, and gear FWD4 can be obtained byenergizing only solenoid FCS.

The aspects of the hydraulic system 210 which enable the hydraulicpressure supplied to the forward and reverse directional clutches FDCand RDC to be modulated in order to provide for smooth, jolt-freegradual engagement of these clutches during gear shifts will now beexplained. The clutch pressure modulation circuit 236 includes pressurereducing valve 240, proportional solenoid valve 22f, and fixed orifice280 interconnected as shown in FIG. 5. The pilot line 282 of pressurereducing valve 240 is located on the downstream side of fixed orifice280, and is connected to the inlet (IN) port of control valve 22f. Valve22f is a normally closed, proportional hydraulic valve which is operatedby solenoid PMS. Solenoid PMS is energized with a proportional signalfrom electronic controller 30 which can vary in average magnitude from0% to 100%, which varies the size of the opening between the input portand output (OUT) port of valve 22f from 0% (no flow or shut condition)to 100% (maximum size orifice or full flow condition). Valve 22fprovides a selectable, controllable size orifice between pilot line andreturn line 284 which leads directly to hydraulic reservoir 214 asindicated. The size of valve 22f and its opening is selected relative tothe size of fixed orifice 280 so that, full or 100% energization ofsolenoid PMS provides a sufficiently large opening between pilot line282 and return line 284 to cause the fluid pressure in pilot line 282 todrop so low that return spring 286 of pressure regulator 240substantially completely closes off fluid flow from high pressure line224 to line 272. Note that in this condition, orifice 280 provides ableed-off for any existing pressure in line 272, which will promptlydrop pressure in all lines and clutches then in fluid communication withline 272 through valve 22d and valve 22e. When the solenoid PMS is onlypartially energized, such as 50%, the size of the opening through valve22f available to drain pilot line 282 is insufficient to allow the fluidpressure to drop enough to cause pressure reducing valve 240 to closecompletely, since some pressure still exists in line 282 and resists theforce of opposing bias spring 286. Accordingly, some fluid is still ableflow through reducing valve 240 and a controlled amount of pressure ismaintained in hydraulic line 272 for regulating engagement of theforward or reverse directional clutch FDC or RDC.

The opening or orifice of a proportional solenoid valve 22f is variabledepending upon the position of its valve spool or solenoid plunger,which is controlled by the electromagnetic field generated by theaverage DC voltage supplied to the proportional solenoid. The voltagesignal applied to solenoid PMS is preferably an alternating electricalsignal, such as a pulse width modulated (PWM) signal having an averageDC value directly correlated to its duty cycle. Fixed orifice 280 issized to restrict the amount of fluid which may flow from hydraulic line272 into the pilot line 282, thereby permitting the variable sizeopening in valve 22f to control the pressure in line 282 and therebycontrol the pressure in main line 272 downstream from reducing valve240.

FIG. 7 is a simplified plan view showing the six solenoid valves 22a-22fand pressure reducing valve 240 mounted on top of a hydraulic manifold300 in close proximity to one another. In particular, the solenoids,such as solenoid FCS and PMS, are in relatively close proximity, thuspermitting magnetic coupling to occur between the solenoid valves whenenergized. In conventional powershift transmissions, the arrangement ofsolenoids in close proximity to one another is not known to pose anyproblem. We have learned that in powershift transmission 20, magneticcoupling between the solenoid FCS and the proportional modulationsolenoid PMS adversely effects the desired operation of the proportionalmodulation valve 22f. For this reason, it is highly desirable to providemagnetic flux compensation to counteract the effect of the undesiredmagnetic coupling between the solenoid FCS and solenoid PMS, which willbe further discussed later.

Controller 30 and Its Electrical Circuits (FIGS. 8 through 13)

FIG. 8 is a block diagram of electronic controller 30 of FIG. 1.Controller 30 includes microcomputer 320 which is comprised of amicroprocessor 322 with crystal oscillator time base 323, random accessmemory (RAM) 324, and a chip select/memory decode (CS/MD) circuit 326.Controller 30 also includes: a U-V erasable, programmable read-onlymemory (EPROM) 330; a power supply circuit 332; a low voltage detectorcircuit 334; a watchdog timer circuit 336; a limp-home relay circuit338; a nonvolatile read/write (R/W) memory 340 in the form of anelectrically erasable, programmable read-only memory (EEPROM); first andsecond buffered input/output (I/O) port circuits 342 and 344 which maytake the form of a Peripheral Interface Adapter (PIA); a programmabletimer module (PTM) 346; an analog-to-digital (A/D) converter circuit348; a transmission solenoid driver circuit 350; an input signalconditioner circuit 352; and a display driver circuit 354.

Microprocessor 322 communicates with the remainder of the circuits andmodules through multiple-line control bus 358, multiple-line address bus360 and multiple-line data bus 362, which are connected as shown. Inputconditioner 352 receives input signals FWD, NEUT and REV from the modeselect control 34, receives UP and DN input signals from pulser selectcontrol 36, receives input signal PB from parking brake control 27, andreceives input signal CL from the manual clutch engagement control 26.These signals are transformed by conditioning circuit 352 into negativetrue digital logic signals FWD*, REV*, UP*, DN*, NEUT*, PB*, and CL* fordelivery to first I/O port 342 through lines 364, as shown. I/O port 342controls and communicates with display driver circuit 354 throughcontrol lines 366. In addition, port 342 communicates serially with andcontrols nonvolatile R/W module 340 via control lines 366.

Potentiometer 44 provides an analog input signal representing theposition of the clutch pedal 42 on line 45. A/D converter 348 is asixteen-channel analog-to-digital input device. It receives the signalon line 45 as an analog input. Converter 348 also receives analog inputsignals from feedback lines 370 from the transmission solenoid drivercircuit 350 and from feedback line 372 from the driver circuit forsolenoid PMS. Converter 348 also receives the filtered supply voltagesignal V_(BBF) as an analog input from line 374. Each of these analoginput signals is connected by a distinct input pin leading to a distinctchannel of A/D converter 348.

The second I/O port 344 provides digital output signals to five outputlines 376 which lead to the inputs of five individual solenoid driversof circuit 350. Module 344 also outputs control signals for the channelselection of A/D converter 348 via multiple control lines 378.

The sixth solenoid, namely the proportional solenoid PMS, is driven by aproportional alternating signal, such as pulse width modulation (PWM)signal from programmable timer module 346 that is output on line 380. Inthe preferred embodiment, the PWM signal on line 380 from programmabletimer module 346 has a constant frequency of 200 Hz when present,generated within module 346 from a 0.9 MHz clock signal received frommicroprocessor 322 via one of the control lines of control bus 358. Thevalue of the duty cycle of the PWM signal is adjusted or updated every10 milliseconds. The accuracy with which the duty cycle may be set oradjusted is dependent upon the frequency of the 0.9 MHz clock signal.The duty cycle of the PWM signal may be varied by adjusting the on-time(i.e., the mark-time of the mark-to-space ratio) of the PWM signal from0.0000% to 99.99998% in increments of 1.1 microseconds (i.e., the periodof the above clock signal) as determined by the value of the lower orderbits loaded in a sixteen-bit register within PTM 346 by microprocessor322.

The microprocessor 322 in a conventional manner periodicallyinterrogates all of the inputs to determine their status, andperiodically updates all outputs. This communication function occursover buses 358 through 362. Selected inputs, such as UP* and DN*, areconnected by lines 364 to the input/output port 342 in a conventionalmanner which allows an interrupt signal (IRQ) to the microprocessor 322via an interrupt line which is part of control bus 358. These interruptsare generated by port 342 upon change of state of any of the lines 364from high to low.

As noted above, transmission solenoid driver circuit 350 receives fivesignals from the second input/output port 344 and one signal from theprogrammable timer module 346. Each of these output signals areconnected to one of the individual driver/amplifiers 382a-382f. Thepreferred embodiment of controller 30, the individual driver outputlines 32a-32f must be grounded to energize their respective solenoidcoil, since the other side of each of the solenoid coils is connected toone of two supply lines 384 or 386 coming from a source of DC supplyvoltage, as will be further explained.

The transmission solenoid driver circuit 350 provides feedback signalson lines 370 to A/D converter 348 which are digitized and then deliveredto the microprocessor 320. Using this feedback information,microprocessor 320 can determine whether the individual solenoids 21 andtheir associated transmission solenoid driver circuits are functioningproperly. Specifically, microprocessor 320 can interrogate the fiveindividual solenoid driver circuits 350a-350e by supplying appropriateaddress and command signals to I/O port 344 and with A/D converter 348,monitor the analog feedback signals on lines 370. Microprocessor 322 caninterrogate the solenoid driver circuit 350f for solenoid PMS by sendingsimilar address and command signals to programmable timer module 346which drives circuit 350f. However, it is still A/D converter 348 whichdigitizes the analog signals on line 370f and 372, and digitizes themfor delivery via data bus 362 to microprocessor 322 for analysis.

The power supply circuit 338 receives a supply voltage V_(BB) appliedacross ground line 386 and line 388, and produces a coarsely filteredsupply voltage V_(BBF) to low voltage detector circuit 334. The powersupply 332 also produces a heavily regulated V_(CC) signal (nominally +5volts DC) on line 392 which supplies power to all of the circuits ormodules 334-354.

Low voltage detector circuit 334 monitors the supply voltage V_(BBF) online 390 and signals microprocessor 320 by a signal placed upon controlbus 358 whenever a low voltage condition is detected, so thatappropriate action may be taken, preferably resetting microprocessor322. Watchdog timer circuit 336 monitors proper operation of thesoftware in a manner well-known to those in the art, namely providing anI/O output command placed at regular intervals within all portions ofthe stored program to reset the timers within circuit 336. Circuit 336includes two timers which must be reset before the expiration of apredetermined interval, such as 20 milliseconds, by a control signaldelivered by line 394 from first I/O port 342. If either one of thetimers within circuit 346 times out on account of failure to receive atimer reset signal on line 394 before the end of the predeterminedinterval, a signal on line 396 resets the microprocessor. If watchdogtimer circuit 336 fails to receive a reset signal on line 394 for aneven longer time interval, such as 320 milliseconds, circuit 336generates a signal on line 398 which causes the power supply 332 tocut-off power to the microcomputer 320 by activating line 400 toenergize the limp home circuit 338.

Limp home circuit 338 contains several relays which are responsivesignals FWD* and REV* derived from the forward and reverse signals frommode select control 34 which enable the energization of the forward andreverse solenoids FCS and RCS and first gear speed clutch solenoid 1SS,but only after mode lever 35 has been placed in its N position and thenshifted to its F or R position. Limp home relay circuit 338 bypasses thedisabled microcomputer 320 by directly actuating the appropriatesolenoids via grounding signals limp home first gear (LH1*), limp homeforward (LHF*), and limp home reverse (LHR*) respectively connected tothe driver/amplifier outputs 32a, 32d and 32e.

Integrated circuits suitable for use in the electronic controller 30 arelisted in Table 3 below:

                  TABLE 3                                                         ______________________________________                                        REF. NO.                                                                              ITEM        MANUFACTURER   PART NO.                                   ______________________________________                                        322     Microprocessor                                                                            Motorola       MC6802                                     324     RAM         Motorola       MC6802                                     326     CS/MD       National       74HC138                                                        Semiconductor                                             330     EPROM       Motorola       MCM2532                                    340     EEPROM      National       NMC9306                                                        Semiconductor                                             342     PIA.sub.1   Motorola       MC6821                                     344     PIA.sub.2   Motorola       MC6821                                     346     P.T. Module Motorola       MC6840                                     348     A/D Converter                                                                             National       ADC0817                                                        Semiconductor                                             ______________________________________                                    

The peripheral interface adapters (PIA) are integrated circuit chips(ICs) used for I/O port 342 and 344 are configured by instructionsreceived from microprocessor 322 when electronic controller 30 isinitially started up in a manner well known to those familiar with theMotorola 6800 Series ICs. The software program used to provide thisinitialization of the I/O ports 342 and 344, as well as the internaloperation of electronic controller 30, and the operation of transmission20 as determined by electronic controller 30 is stored in the ROM chip330. The techniques used to program the Motorola 6800 Seriesmicroprocessor and related chips are well understood, and need not bedescribed here, beyond describing the novel functions implemented bycontroller 30 which are described more fully below.

FIGS. 9 and 10 show a preferred embodiment of input signal conditionercircuit 352. In FIG. 9, five proximity switches 410-416 and 46 are shownwhich respectively produce the signals FWD*, REV*, UP*, DN* and CL*.Each of these switches are connected at one end thereof to ground line386 and at the other end thereof to a pull-up resistor such as resistor422 which is connected to the voltage supply source V_(CC) on line 392.Each switch 410-416 has a normally open contact which is connected toground on line 386 when a magnet is placed in close proximity to theswitch.

FIG. 10 shows the opto-isolator circuits 430 and 432 respectively usedto condition signals from limit switch contacts 28a and 27a and producethe input signals NEUT* and PB*. Both circuits are identical inoperation, and so only one of the circuits will be described. Circuit430 includes opto-isolator unit 434 including photodiode 436 andphototransistor 438. Diode 440 protects photodiode 436 againstaccidental breakdown due to any reverse overvoltage which might beapplied, while current-limiting resistor 442 ensures the photodiode 436does not see excessive current during forward-biased operation. Pull-upresistor 444 is connected between the voltage supply V_(CC) on line 392and the collector of phototransistor 438 switch 28 is actuated as shownwhen mode lever 35 is in its N position. When switch 28 is released, itscontact 28a is open and phototransistor 438 is off. Line 446 thus floatshigh (to the voltage level of supply V_(CC)). When it is in neutral,switch 28 is actuated as shown is closed, photodiode 436 andphototransistor 438 turn on, which sinks line 446 to near groundpotential. Parking brake switch 27 is actuated and its contact 27a isclosed when the parking brake lever 31 is applied. When contact 27a isclosed, opto-isolator unit 432 is turned on, thus causing line 448 to beat near ground potential. When parking brake lever 31 is released,contact 27a is open, and line 448 floats high near the voltage level ofsupply V_(CC).

FIG. 11 shows one possible mechanical construction for manual clutchengagement control 26. As partially shown in FIG. 11, control 26includes lever 460 of clutch pedal 42 shown in FIG. 1. Lever 460 ismounted at its lower end to a shaft 462 to permit pivoting of lever 460about the axis defined by shaft 462. A torsion spring assembly (notshown) mounted on the shaft 462 normally biases lever 460 in a clockwisedirection upward toward the position defined by positive stop 464. Lever460 has an outwardly extended flange 466 which carries permanent magnet468. Clutch position sensor 46 is mounted on stationary bracket 470 sothat magnet 468 is positioned adjacent to sensor 46 when lever 460 is inits normal upward position.

When the driver depresses the clutch foot pedal 42, lever 460 rotates incounterclockwise direction about the axis defined by shaft 462. Thiscauses magnet 368 to move away from sensor 46, thus causing a change inthe output of the sensor as soon as the driver begins to depress thepedal. The movement of the lever 460 in the counterclockwise directionis limited by stop 472. When the clutch pedal is fully depressed (asshown in phantom in FIG. 11), flange 466 engages roller 25a of powerswitch 25, thus actuating switch 25. As has been discussed previously,the normally closed contact of power 26 permits power to be supplied tothe +12 volt supply line 23 to solenoid valves 22a-22f (as best shown inFIG. 1). When the flange 466 engages roller 25a it causes power switch26 to open, thus deenergizing solenoid valves 22a-22f which causestransmission 20 to shift to neutral. Rotary-style potentiometer 44 issuitably coupled to lever 460 in a manner that makes its rotary shaftcoaxial with the axis of shaft 462, thus allowing pot 44 to produce ananalog signal on line 45 which varies linearly as a function of rotationangle of lever 460.

FIG. 12 shows one possible circuit 480 interconnecting the variousswitches which provide power to the solenoids of valves 22, power supply332 and vehicle starter circuitry. The components within dotted block482 are part of power supply 332 shown in FIG. 8. Switch 24 isthree-position switch, with its three positions from left to right being"OFF, ON and IGNITION (IGN)." The left (OFF) and center (ON) positionsare detented, while the right (IGN) position is spring returned to thecenter position. In FIG. 12, two contacts 24a and 24b of switch 24 areshown. When switch 24 is in its OFF position, contact 24a is open, andwhen switch 24 is in the other two positions contact 24a is closed.Contact 24b is closed only when switch 24 is in its IGN position. Switch25 is actuated, and its normally closed contact shown in FIG. 12 isopen, only when clutch pedal 42 is fully depressed. Contact 27b ofparking brake switch 27b is open any time parking brake lever 31 isapplied, but is otherwise closed as shown in FIG. 12. Contact 28b ofneutral safety start switch 28 is closed only when mode lever 35 is inneutral, while an contact 28c is open only when mode lever 35 is inneutral. Those skilled in art will readily understand under whatconditions the power may flow to the starter circuitry to line 486connected to solenoids 1SS, 2SS and 3SS, and to line 488 connected tosolenoids RCS, FCS and PMS. The diode 492, the choke 494 and varistor496 are all provided to help protect electronic controller 30 againstaccidental reverse voltages and voltage spikes.

FIG. 13 is a detailed schematic diagram of the components used in thepreferred embodiment of two individual transmission solenoid drivercircuits, namely circuit 350d used to operate the forward clutchsolenoid (FCS) of valve 22d, and driver circuit 350f used to operate theproportional modulation solenoid PMS of valve 22f. Each of the othersolenoid drivers 350a through 350e is identical in construction tosolenoid driver circuit 350d.

Solenoid driver circuit 350d includes amplifier 382d, which in thepreferred embodiment of the present invention includes a Darlington pairpower transistor 500 having its base terminal 500b connected to anoutput of I/O port 342 through resistor 502, its collector terminal 500cconnected to solenoid control line 32d, and its emitter 500e connectedto ground. Preferably, transistor 500 has a gain of about 2,200 and afive amp output capacity, thereby providing, when turned on, sufficientdraw between collector 500c and emitter 500e to energize solenoid valve22d. Connected between collector 500c and emitter 500e are diode 504,varistor 506 and capacitor 508. Diode 504 and varistor 506 protecttransistor 500 against overvoltage conditions and inductive surges,especially those which occur when drive transistor 500 is turned off andthe energy stored in the magnetic field about energized solenoid 22d israpidly discharged. Capacitor 508 provides protection for amplifier 382dfrom radio frequency interference, ringing and other high frequencytransients.

The solenoid driver circuit 35d also includes a feedback circuit bywhich the microprocessor 322 can monitor the operation of solenoid valve22d and amplifier 382d. The feedback circuit includes a voltage dividermade up of resistor 512 and 514 which is tapped at its center by line516 to obtain a signal passed through resistor 518 to line 370d leadingan input terminal of A/D converter 348. Zener diode 520 protects againstvoltage spikes to the input terminal of A/D converter 348. The feedbackcircuit permits monitoring of the solenoid 22d and its drive circuit382d to ensure that they are operating as commanded.

Driver circuit 350f for solenoid 22f is very similar to the drivercircuit 350d just described. Accordingly, only the differences betweenthe two circuits will be explained. The input to amplifier 382f comes,not from second I/O port 342, but instead from a single line output ofthe programmable timer module 346. Pull-up resistor 532 is connected tothe supply line V_(CC) to keep line 530 high except when it isintentionally pulled low by output pin 3 of module 346. Buffer amplifier534 inverts the signal on line 530 and delivers it through resistor 536to the input terminal of Darlington pair power transistor 540 ofamplifier 382f. The signal on line 538 is a positive logic version ofthe negative logic PWM signal produced by the programmable timer module346, which operates under control of the microprocessor 322. As is wellknown to those in the art, a PWM signal alternates between two voltages(e.g., the supply voltage and ground) at a relatively high frequency,and has an average DC value proportional to its duty cycle, which canvary from 0% to 100%. Signal 538 rapidly turn amplifier 382f on and off,so that the solenoid control line 32f is also rapidly turned on and off,thus applying alternating PWM signal across the solenoid coil PMS whichhas an average DC value proportional to the duty cycle of the PWMsignal. The voltage on line 32f is monitored by input pin 6 of the A/Dconverter 348 which receives a scaled-down voltage signal from line 370fwhich is connected through resistor 541 to the voltage divider made ofresistors 542 and 544.

An additional feedback circuit 550 is provided in conjunction withdriver circuit 350f in order to be able to monitor the amount of currentactually flowing through the solenoid PMS. It is desirable to monitorthe current flowing through solenoid PMS since this current is directlyproportional to the magnetic flux responsible for moving and preciselypositioning the solenoid plunger valve spool assembly of valve 22f thatdetermines the precise size of the variable orifice in valve 22f.Circuit 550 includes precision shunt resistor 532 having a very lowresistance (e.g., 0.22 ohms) in series between ground 386 and theemitter of power transistor 540 to provide a voltage signal at node 554which is directly proportional to the amount of current flowing throughsolenoid PMS. This voltage signal is delivered to an analog input (pin12) of A/D converter 348, but preferably not until it is amplified byamplifier circuit 556, which may have a gain of about seven, asdetermined by feedback resistor 558 and connected between the output andnegative input of operational amplifier 560, and by resistor 559connected between the negative input and ground. This amplificationgives the feedback signal from node 554 greater dynamic range at line555, thus effectively increasing the sensitivity of A/D converter 348with respect to detecting differences in the current flowing through thecoil of solenoid PMS. Resistor 562 and capacitor 564 form a low-passfilter to remove unwanted high frquency noise from line 566 connected tothe positive input of amp 560.

Also shown near the bottom of FIG. 13 is a preferred signal conditioningand feedback circuit 570. Circuit 570 provides a scaled-down DC signalof the DC voltage signal V_(BBF) from line 390 (which in turn isdirectly proportional to the DC voltage signal V_(BBG) on line 488 whichsupplies DC power to solenoid PMS) to an analog input (pin 10) of A/Dconverter 348. Resistor 572 and 574 form a voltage divider network whichscales down the V_(BBF) signal to a suitable voltage range on line 576for examination by A/D converter 348. Zener diode 578 protects the inputcircuit connected to pin 10 and within A/D converter 348 from transientovervoltages.

Software and the Controlling of Clutch Engagements (FIGS. 14 Through 18)

As will be readily appreciated by those in the art, the microprocessor322 shown in FIG. 8 runs under control of a stored program placed in ROMmodule 330. The characteristics of the stored program important to anunderstanding of the present invention will now be explained withreference to figures which follow along with some general informationregarding selected functions of the stored program. FIG. 14 is ageneralized software flowchart which shows the five major segments ofsoftware code which makes up this stored program and their basicinterrelationship. The five major sections are: restart code 580;neutral code 582; forward code 584; reverse code 586 and non-maskableinterrupt (NMI) code 588. After a power-up indicated by arrow 590,detection of a low-voltage condition by detector circuit 334 asindicated by arrow 591 from input block 592, or watchdog timer 336 timesout as indicated by arrow 593 from input block 594, microprocessor 322is reset, as indicated by oval block 596. This causes microprocessor 322to begin executing the restart code 580. During this time, the state ofmode and pulser levers 335 and 337 are ignored, and all transmissionsolenoid valves 22 are turned off. Also, the following transparentelectronic hardware tests and hardware configuration and initializationoperations are performed: (a) the check sum of EPROM 330 is tested; (b)RAM 324 of microprocessor 322 is tested and cleared; (c) the twoperipheral interface adapters 342 and 344 are tested and configured; and(d) the programmed timer module 346 is tested and configured. Uponcompletion of the restart sequence, the controller 30 will default tothe limp home mode if any hardware problems were detected, and willprovide an error code on display 50 if the mode lever 35 is out of theneutral position. If no hardware problems were detected by themicroprocessor 322, and the mode lever 35 is in neutral, themicroprocessor 320 will pulse a positive number, and then a negativenumber representing the forward and reverse gears (if any) which werestored in non-volatile memory 340 as a result of the memory gearfeature.

The memory gear feature is the storage and recall of the last gear thatthe controller 30 had the transmission 20 in when power was last removedfrom the controller. In particular, controller 30 retains theshuttle-shift gear combination present at the time that power wasremoved in EEPROM 340. The shuttle-shift gear combination stored by thememory gear feature in memory 340 is preferably displayed only the firsttime that the controller 30 is in neutral after a power-up situation.

After the restart code 580 has been executed once, the controller 30 isturned over to the control of the neutral code 582. While executing, theneutral code 582 and the forward and reverse codes 584 and 586periodically check the status of mode lever 35, as indicated by decisiondiamond 598 in FIG. 14, and the logic flow paths 602, 604 and 606therein. When microprocessor 322 is executing the neutral code 582,controller 30 is said to be in the system neutral mode. In this mode,the speed clutch solenoid for the current gear pattern displayed ondisplay 50 remains energized and all other transmission solenoids areoff. The display 50 is caused to display the shuttle-shift gearcombination for the last gear that the transmission 20 was engaged priorto entering neutral in according to controller 30. The display of theshuttle-shift gear combination preferably occurs as follows: (a) theforward speed gear is displayed (e.g., "-2") for a first predeterminedtime interval; (b) the display 50 is cleared for a second predeterminedinterval; (c) the reverse speed gear is displayed (e.g., "-2") for athird predetermined interval; and (d) the display 50 is cleared for thesecond predetermined time interval; and (e) the sequence returns to step(a). All of these predetermined time intervals may be 0.5 seconds, ifdesired. The neutral mode is exited by the shifting of the mode lever 35to either its forward position or its reverse position.

When the mode lever 35 is shifted to its forward position,microprocessor 322 begins to execute the forward code 584, and thecontroller 30 is said to be in the forward mode. In this mode,controller 30 allows the transmission 20 to operate in the forwarddirection in all forward gears (i.e., gears 1, 2, 3 and 4). As soon asthe mode lever 35 is moved into its F position, the controller 30engages the transmission 20 by turning on the appropriate speed clutchsolenoid and the forward direction solenoid immediately. Gradualengagement of the forward directional clutch provides for smoothshifting from neutral into gear, or from one forward gear to anotherforward gear by either upshifting or downshifting. This gradualengagement is achieved by execution of a portion of the code known asthe "PWM sequence," which will shortly be described. When in the systemforward mode, display 50 preferably continuously displays the forwardgear of operation, and updates the display periodically, and with everygear upshift or downshift.

If the mode lever 35 is placed into its reverse position, microprocessor322 begins to execute the reverse code 586. When the microprocessor 322is executing this code, and the controller 30 is said to be in thesystem reverse mode, which allows the transmission 20 to be operated inthe reverse direction in all reverse gears (i.e., gears 1, 2, 3 and 4).When in this mode, display 50 preferably continuously displays theselected reverse gear of operation, periodically updating the displayespecially with every change of gear. After the mode lever 35 is movedinto its R position, the transmission 20 is engaged by the controller 30in the reverse mode by turning on the appropriate speed clutch solenoidand the reverse clutch solenoid immediately. Gradual engagement of thereverse directional clutch RDC provides for smooth shifting from neutralinto gear, or from one reverse gear to another reverse gear by eitherupshifting or downshifting. The PWM sequence code is executed to providethis gradual engagement.

In the system forward mode and the system reverse mode, the actuation ofthe pulser lever into its UP position or DN position will cause a singleupshift and or a single downshift respectively. Successive upshifts areallowed in either the system reverse or forward mode until the highestgear, which is fourth gear in the preferred embodiment of transmission20, is obtained. Successive downshifts are also allowed in the systemforward or reverse mode until the lowest gear, namely the first gear, isobtained. When controller 30 receives an upshift request by the movementof pulser lever 37 from its N to UP position, the microprocessor 322will not generate an upshift command until the pulser lever 37 hasremained in the UP position for a predetermined minimum number ofmilliseconds such as 50 milliseconds. After the controller 30 completesan upshift, a delay of another predetermined period of time, such as 0.5seconds, is preferably required before another shift request will beallowed to occur. While the controller 30 is in the process of engaginga new gear, the display 50 will reflect the newly selected gear to whichthe transmission is being shifted.

If the mode lever 35 is in neutral, and a upshift (or downshift) requestis received, the speed clutch solenoids will be energized (andde-energized) as required to match the requested gear. All othersolenoids will remain unaffected.

The NMI code 588 is used to update the various software and hardwaretimers used within the controller 30. It is also used to update the timedelays used to generate the PWM signal produced by programmable timermodule 346 that is used to operate solenoid PMS. The NMI code 588 isexecuted whenever the microprocessor 322 receives a non-maskableinterrupt from the programmable timer module 346, which occurs at 10millisecond intervals. The execution of any code then executing will besuspended and control passes to the NMI code 588 as indicated by dottedlines 608 in FIG. 14. Once control has been passed to the NMI code 588,the microprocessor 322 will not allow the code to be interrupted by anyother interrupt which may be received, since doing so would eventuallyskew the various timers and the external time base in PTM 346 used byfor microprocessor 322. The execution of the NMI code 588 takes arelatively short period of time to execute. Once the NMI code 588 hasbeen executed, control is passed back to the code segment which wasinterrupted, as indicated by dotted lines 609.

Referring now to FIG. 15, the PWM sequence used whenever shifting fromneutral into a forward or reverse gear, or whenever upshifting,downshifting or shuttle-shifting, will be explained. The PWM sequencewill not occur if mode lever 35 is in its N position when an upshift ordownshift request is received. The PWM sequence is preferably set up asa subroutine callable from the forward code 584 and reverse code 586,which is called and executed whenever a certain bit flag is set. The bitflag is set whenever microprocessor 322 recognizes from changes in theinput signals UP*, DN* or transitions from the neutral code to forwardcode or the neutral code to the reverse code that the driver hasrequested any of the foregoing shifts. The execution of the PWM sequenceresults in the delivery of a PWM signal on line 380 to solenoid drivencircuit 350f which energizes the coils of solenoid PMS in a controlledmanner so as to reduce the hydraulic pressure being applied to theappropriate directional clutch which is engaging, or being allowed tore-engage, in order to provide a smooth transition from neutral or theprevious gear to the desired gear.

For the sake of simplicity and ease of understanding the time diagram ofFIG. 15 will be explained by way of example, namely the response ofcontroller 30 to an operator request for a shift from neutral to adesired forward gear. The heavy line 612 represents the average value(or duty cycle) of the PWM signal applied on line 380 to driver circuit350f for driving solenoid PMS. At time t0, a shift request occurs, andthe controller 30 energizes the appropriate speed gear and directionsolenoids immediately. Energization of the proportional solenoid PMS isdelayed for a first period of time and remains at 0% duty cycle at linesegment 614 shown on FIG. 15 as the period T₁ between times t0 and t1.In a preferred embodiment of the present invention, the allowed range oftime for this delay is 0 to 200 milliseconds, which is selectable in 10millisecond intervals due to the time base used by PTM 346. The purposeof this delay T₁ is to allow the filling of the speed gear clutch packand the directional clutch pack with hydraulic fluid before theproportional solenoid PMS is energized to reduce the hydraulic pressureto the directional clutch being engaged. As may best understood byreferring to the hydraulic diagram in FIG. 5, the delay T₁ permits theselected speed clutch and the directional clutch to fill with hydraulicfluid using the substantially the entire fluid output of the hydraulicpump 184, thus minimizing the amount of time required to fill theclutches to be engaged. Thus time delay T₁ may conveniently be referredto as the clutch pack fast-fill delay.

At time t1, the proportional solenoid PMS is energized with a PWM signalhaving a 100% duty cycle which lasts as shown by line segment 616 untiltime t2 is reached. This second time delay T₂ may also be adjusted toany desired value in ten millisecond increments. In the preferredembodiment of transmission 20, the time delay T₂ has a value of 70 to 80milliseconds. The 100% duty cycle effectively provides a DC voltagesignal to the solenoid PMS which is substantially equal to the DC supplyvoltage V_(BBG) provided on line 386, as shown in FIGS. 8, 12 and 13. Inthe preferred embodiment of transmission 20, the solenoid PMS has anominal full voltage rating approximately or substantially equal to thenominal voltage value for the vehicle supply voltage, e.g., 12 volts DC(or 24 volts DC) depending upon the particular vehicle. The purpose ofthis second time delay T₂ is to provide sufficient time to allow astabilized reading of the current passing through the solenoid coil PMSin response to a DC voltage signal of known magnitude to be taken. Thecurrent reading is taken at the end of time delay T₂ by measuring thevoltage across shunt resistor 552 using feedback circuit 550 and A/Dconverter 348 as already explained with respect to FIG. 13. This currentreading is used by microprocessor 322 in its calcualtions to compensatefor the effect of variations in the temperature of solenoid 22f and thetemperature of the hydraulic fluid in transmission 20. These effects andthe temperature compensation techniques employed by controller 30 willbe explained in detail shortly.

At time t2, the proportional signal supplied to the coil of solenoid PMSis reduced down to a calculated value as shown at point 620 in FIG. 15,which has a magnitude which for convenience will be called DC-MAX. Thevalue DC-MAX is calculated in accordance with formulas which will laterbe described. Briefly, the point DC-MAX represents the value at whichthe solenoid valve 22f must be operated in order to achieve a hydraulicpressure in the directional clutch at which sliding friction just beginsto occur (or is about to occur) within its clutch pack, that is thepressure at which the clutch just begins (or is about to begin) initialsliding engagement where minimal torque transfer occurs. The value ofDC-MAX is inversely proportional to the hydraulic pressure achieved bythe clutch modulation pressure circuit 290 shown in FIG. 5. To achieve asmooth engagement, the average value or duty cycle of the PWM signal issteadily decreased as indicated by sloping line segment 622, so that thehydraulic pressure being applied to the directional clutch will steadilyincreases over a predetermined period of time T₃ between times t2 andt3. Once time delay T₃ is over at time t3, the duty cycle of the PWMsignal being applied to the coil of solenoid PMS is reduced to 0% if itis not already at 0%. To achieve gradually increasing clutch pressurefrom time t2 to time t3, the gradually decreasing duty cycle ispreferably reduced at a substantially linear rate of decay. The slope ofthe line segment 622 is the decay rate DR, and may be adjusted toachieve the desired speed of engagement while not creating unacceptabletorque spikes or jolts. Alternatively, it may be set to allow a linearchange between a DC-MAX value and a predetermined ending value of linesegment 622 at time t3, such as zero to 40% duty cycle. For thepreferred embodiment of transmission 20, the rate DR is set at somevalue between 4.5% and 27% per second, and the time delay T₃ may be setto 1.5 seconds. If the directional clutch is not already fully engagedat time t3, the reduction of the duty cycle to 0% ensures that fullhydraulic pressure is then applied to the clutch, thereby fully engagingthe clutch.

In the preferred embodiment of the controller 30, the length of the timedelays T₁, T₂ and T₃ are all variable either at the factory or in thefield, or both. Typically the time delay T₁ may vary between 0 and 200milliseconds. The time delay T₂ may be set as desired, for example, from0.0 to 200 milliseconds, and the time delay T₃ may be varied from 0.1seconds 10.0 seconds (or more) if desired. Also, the slope DR may bevaried between minimum and maximum values as previously explained. Thevalues of the time delays T₁, T₂ and T₃ and the decay rate DR are allpreferably predetermined values which are stored in read-only memory 330as fixed values. However, if desired, the values can be made morereadily adjustable in the field by storing them in nonvolatileread/write memory 340 and providing keypad means or the like forprogramming them in the field, or by providing adjustable potentiometersor DIP switches which are manually set to a position corresponding tothe desired value. Several potentiometers, which were read as analoginputs by A/D converter 348, were used in early prototypes of controller30 to facilitate experimentation into the effects produced by varioussettings of DC-MAX, T₁, and DR upon the operation of transmission 20.Laboratory and/or field tests may be conducted for each type oftransmission 20 installed in a specific type of vehicle to determine theoptimal values of DC-MAX T₁, T₂, T₃ and DR for each gear shift or classof different shifts for the transmission/vehicle combination as will beexplained with respect to FIG. 18.

An explanation of how reading of the current flowing through the coil ofsolenoid PMS provides temperature information will now be given. Theresistance of the coil of solenoid PMS changes considerably as afunction of temperature. In particular coil resistance increaseslinearly as temperature increases. Thus, a steady signal applied to thesolenoid PMS will produce a current through the solenoid coil whichvaries inversely with the operating temperature of the solenoid. Sincethe solenoid PMS is mounted on value 22f in close proximity to thetransmission 20, and since hydraulic fluid regularly flows through valve22f, the temperature of the solenoid coil provides an approximateindication of the actual operating temperature of the transmission 20.Accordingly, by measuring the current flowing through the coil ofsolenoid PMS in response to a steady voltage signal of predeterminedmagnitude, an indication of the temperature of transmission 20 can beobtained. In particular, the actual current obtained in response to thisknown temperature can be compared with the current which would beexpected in response to the same signal applied when the transmission 20is at its nominal operating temperature. The difference between theactual current reading and expected current reading varies inverselywith the change in temperature from the nominal operating temperature ofthe transmission 20. The electronic controller 30 of the presentinvention includes all of the hardware requirements for determiningapproximately the actual temperature of transmission 20 or of solenoidPMS, if so desired. However, in the preferred embodiment of controller30, the approximate actual operating temperature of the transmission 20is never directly calculated, since this information is not needed inorder to provide the desired temperature compensation function. Instead,the actual sensed current provided in response to the time delay T₁ isdetermined in a manner which will be further explained, and is comparedagainst a nominal current value, which nominal value preferablyrepresents the current expected when the transmission 20 is at itsnormal operating temperature.

In order to achieve a stabilized reading of current flowing through thecoil of a proportional solenoid in response to a signal of knownmagnitude which faithfully relates to coil resistance, and therefore tothe temperature of the coil, we determined that the current measurementmust be made using a steady-state signal, preferably a full-voltage DCsignal, rather than an alternating signal. Changing inductive effectsdisturbs the accuracy of the current reading when an alternating signalis used. In particular, a signal which allows the solenoid plunger tomove unpredictably and continually change the effective inductance ofthe coil is troublesome. To achieve the DC signal preferred for readingcurrent proportional to coil resistance, the proportional modulationcircuitry of the present invention is commanded to produce temporarilyduring time delay T₂ a 100% duty cycle signal, which is effectively a DCsignal over the time range of interest needed for making ourmeasurement. If a current reading is taken when the solenoid plunger isstill moving, it will not yield a stabilized current reading.Accordingly, the length of the time delay T₂ should be long enough topermit the solenoid plunger/valve spool to settle into its full-oncondition and allow the transient currents associated with the changinginductance of the solenoid coil to substantially decay away before thecurrent reading is taken. With the particular solenoid coil used inprototypes of transmission 20, transient current conditions wereobserved between up to 60 milliseconds after time t1. At 80milliseconds, the current flowing through solenoid PMS is risingsteadily at the exponential decay rate and is with in a few percent ofits maximum final value. Thus, we found it best in prototypes oftransmission 20, to take the current reading then at 80 millisecondsafter time t1 which we used as the value of our preferred time delay T₁.

One important advantage of obtaining an indication of temperature oftransmission 20 in the foregoing manner is that a separate temperatureprobe and circuit need not be supplied, thus saving cost and increasingsystem reliability. Another significant advantage is that the effect oftemperature changes on the performance of the transmission 20, due tochanging viscosity of the hydraulic fluid or other factors, can becompensated for at the same time that changes in coil resistance ofsolenoid PMS are compensated for. By appropriately adjusting the dutycycle of the PWM signal used to drive solenoid PMS smooth clutchengagements can be provided, not only during operation at normaltemperatures, but also immediately upon vehicle start-up, and whiletransmission 20 is warming up, in cold, warm or hot weather.

In addition to adjusting the values of delay times T₁ and T₃ and decayrate DR, the microprocessor 322 also adjusts the value of DC-MAX tocompensate for changes in temperature of the solenoid PMS and thehydraulic fluid in transmission 20, and variations in the voltagesupply, and variations in the magnetic flux coupling which can existbetween the solenoid(s) adjacent to solenoid PMS. The motivation forcompensating for temperature has been explained above. The motivationfor compensating for variations in the voltage supply is to avoid havingsuch variations unintentionally affect the clutch engagement pressure asdetermined by the operation of solenoid PMS. To lower cost and at thesame time increase reliability, the controller 30 of the presentinvention does not use a separate highly regulated voltage supply toprovide a controlled source of DC electrical power to the seriescombination comprised of solenoid PMS and its driver circuit 350f. Themagnetic flux compensation is highly desirable to compensate for theeffect upon solenoid PMS of the impingement of magnetic flux fromsolenoid FCS, which is generated whenever solenoid FCS is in itsenergized state, and which alters the intended position of the solenoidplunger of solenoid PMS as controlled by the PWM signal passedtherethrough.

The three foregoing types of compensation used to alter the value ofDC-MAX will now will be explained by reference to Equations 1 through 5and 9 of the equations set forth in Table 4 below.

                  TABLE 4                                                         ______________________________________                                        DC-MAX =    D.sub.NSV + T.sub.CF + V.sub.CF                                                              (1)                                                D.sub.NSV = D.sub.ISV + M.sub.CF                                                                         (2)                                                T.sub.CF =  K.sub.T [(I.sub.N - I.sub.A)/I.sub.N ]                                                       (3)                                                V.sub.CF =  K.sub.V (V.sub.N - V.sub.A)                                                                  (4)                                                M.sub.CF =  K.sub.M (F.sub.ON)                                                                           (5)                                                D.sub.ISV = D.sub.MSV + D.sub.FA                                                                         (6)                                                K.sub.T =   K.sub.TSV (K.sub.TFA - K.sub.TFC)                                                            (7)                                                K.sub.V =   K.sub.VSV + K.sub.VFA                                                                        (8)                                                I.sub.A =   K.sub.I (ADCH14/R.sub.SH)                                                                    (9)                                                ______________________________________                                    

For ease of understanding the formulas, a brief explanation of eachvariable used in the nine formulas above is provided in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        SYMBOL  BRIEF DESCRIPTION                                                     ______________________________________                                        ADCH14  Analog voltage value (sensed on channel 14 of A/D                             converter 348 - see FIG. 13)                                          DC-MAX  Initial duty cycle of PWM signal at time t2 (or time                          t6) during PWM sequence                                               D.sub.FA                                                                              Field adjustment to D.sub.MSV                                         D.sub.ISV                                                                             Initial starting value for DC-MAX (before any                                 compensation)                                                         D.sub.MSV                                                                             Starting value for DC-MAX (before field adjust-                               ment, if any)                                                         D.sub.NSV                                                                             Nominal starting value for DC-MAX (before tem-                                perature and voltage compensation)                                    F.sub.ON                                                                              A binary variable (equal to "1" when solenoid FCS is on, and "0"              when solenoid FCS is off)                                             I.sub.A Actual current value (read at end of time delay T.sub.1)              I.sub.N Nominal current value - a constant (equal to current                          produced when full voltage DC signal applied to                               solenoid PMS at the end of time delay T.sub.1 at a known                      temperature)                                                          K.sub.I Constant for scaling voltage-to-current conversion to                         obtain I.sub.A                                                        K.sub.M Constant for scaling M.sub.CF                                         K.sub.T Constant for scaling T.sub.CF                                         K.sub.TFA                                                                             Field adjustment to K.sub.TSV                                         K.sub. TFC                                                                            Field constant used in field adjustment of K.sub.T                    K.sub.TSV                                                                             Starting value for K.sub.T (before field adjustment,                          if any)                                                               K.sub.V Constant for scaling V.sub.CF                                         K.sub.VFA                                                                             Field adjustment value for K.sub.V                                    K.sub.VSV                                                                             Starting value for K.sub.V                                            M.sub.CF                                                                              Magnetic (flux) compensation factor                                   R.sub.SH                                                                              Value of shunt resistor 552 in ohms (see feedback                             circuit 550 - FIG. 13)                                                T.sub.CF                                                                              Temperature compensation factor                                       V.sub.A Actual voltage reading (equal to present value of                             V.sub.BBF)                                                            V.sub.CF                                                                              Voltage compensation factor                                           V.sub.N Nominal voltage value - a constant (equal to nominal                          value of V.sub.BBF)                                                   ______________________________________                                    

Equation 1 represents the final equation solved by microprocessor 322 isorder to calculate the value of DC-MAX. DC-MAX is a combination of threevalues, namely D_(NSV), the nominal starting value for DC-MAX, andT_(CF) and V_(CF), the compensation factors for temperature and voltagerespectively. As shown in Equations 2 and 5, the nominal starting valueD_(NSV) for DC-MAX includes the magnetic compensation factor M_(CF). Thevariable M_(CF) has a value of 0 or a constant K_(M), depending upon thestate of binary variable F_(ON). Variable F_(ON) is set to unity bymicroprocessor 322 when the solenoid FCS is energized, and is set tozero when the solenoid FCS is deenergized. Accordingly, the magneticcompensation factor M_(CF) has a nonzero value only when solenoid FCS isenergized.

Equation 3 shows how the value of temperature compensation factor T_(CF)is calculated. The constant I_(N) represents the nominal current valuethat is produced at the end of time delay T₁ when a full voltage DCsignal (at the nominal voltage rating of V_(BBG)) is applied to solenoidPMS at a known temperature and with solenoid FCS deenergized. Thisconstant value may be determined by experimentation. The actual currentvalue I_(A) represents the current read at the end of time delay T₁. Aspreviously explained with respect to FIG. 13, this current reading isobtained by passing the current flowing through solenoid PMS across aprecision shunt resistor 552, amplifying it and presenting to channel 14of A/D converter 348. Equation 9 shows the typical form of scaling andconversion of the digitized voltage reading obtained by A/D converterfrom its input channel 14 to the value I_(A) used by microprocessor 322.The expression within brackets in Equation 3 is a decimal fractionindicating the amount of deviation of the actual current reading fromthe nominal current reading. The value of the expression within bracketsis then multiplied by constant K_(T) to scale the value of the bracketedexpression as is required to produce the correct temperaturecompensation factor for the particular type of solenoid used forsolenoid PMS and the type of hydraulic fluid in use in transmission 20.An appropriate value for scaling constant K_(T) can be determined byexperimentation, or by calculation (if the temperature coefficient ofthe coil resistance of solenoid PMS and the temperature coefficient forhydraulic fluid viscosity and its effect upon the intended operation ofhydraulic fluid 210 of transmission 20 is known).

Equation 4 provides the calculations performed by microprocessor 322 inorder to compute the voltage compensation factor V_(CF). In Equation 4,the nominal voltage value V_(N) is a constant corresponding to thenominal value of coarsely filter supply voltage V_(BBF). The actualvoltage V_(A) in Equation 4 is equal to the present value of supplyV_(BBF) as determined by the operation of voltage feedback circuit 510in conjunction with input channel 12 of A/D converter 348, as shown inFIG. 13. Those in the art will appreciate that it may be necessary toscale the digitized value received from analog input channel 12 of A/Dconverter 348 to obtain a value for V_(A) actually equal to the presentvalue of voltage V_(BBF). In Equation 4, the difference between valuesV_(N) and V_(A) is multiplied by scaling constant K_(V) to obtain thevoltage compensation factor V_(CF) used in Equation 1.

As illustrated by Equations 7 and 8, the scaling factors used in theequations, such as Equations 3 and 4, can be them themselves variablesif desired. This is preferred as a technique for the initial fine-tuningof controller 30 to a particular transmission 20, and for fine-tuningcontroller 30 when used in combination with transmission 20 on aparticular off-road vehicle. The vehicle's weight and loads and thedynamic operating conditions desired for transmission 20 can varyconsiderably, depending upon the particular vehicle and even upon theagricultural, construction or mining purpose to which the vehicle willbe principally directed. Accordingly, we initially provided means in ourprototypes for allowing the scaling factors, such as factors K_(T) andK_(V), to be adjusted with relative ease in a manner previouslydescribed using potentiometers or the like. Equations 7 and 8demonstrate two different techniques for permitting field adjustment ofthese scaling factors. In Equation 8, the starting value K_(VSV) of thevoltage compensation scaling factor K_(V) is permitted to be adjustingby summing a field adjustment value K_(VFA) with the starting valueK_(VSV). It is preferred that microprocessor 322 be programmed to onlyallow the field adjustment value K_(VFA) to have a value equal to apositive or negative predetermined decimal fraction of the startingvalue K_(VSV), such as 0.3, thus limiting the amount of field adjustmentwhich is permissible to be with a reasonable minimum and maximum. InEquation 7, the starting value K_(TSV) for the temperature compensationscaling factor K_(T) is adjusted by being multiplied by the differencebetween a field adjustment value K_(TFA) and a center range constantK_(TFC). The operation of the Equation 7 adjustment is best understoodby considering an example where the field adjustment value K_(TFA) mayrange between 0 and 20. The value of K_(TFC) would then preferably beselected within the center of this range, i.e. 10, thus allowing thetemperature compensation factor K_(T) to be adjusted over any extremelywide positive or negative range, if desired. If such a wide range ofadjustment is not desired, the predetermined minimum and maximum valuesof field adjustment value K_(TFA) and the fixed value for the centerrange constant K_(TFC) may be reduced to produce any desired range ofallowable adjustment between a minimum and maximum for factor K_(T).

FIG. 16 is a detailed software flowchart showing the general features ofthe PWM sequence of operations carried out by microprocessor 322 underthe control of the stored program and in response to a shift request,including reference to the calculation of the maximum duty cycle valueDC-MAX just explained. On receiving a shift request as indicated by ovalblock 650, microprocessor 322 determines which speed clutch solenoid anddirectional clutch solenoid value to energize as indicated in block 652,and turns them on immediately as indicated by output blocks 654 and 656at time t0. Then, as indicated by decision block 658, microprocessor 322waits for the clutch pack fill delay (time delay T₁) to be over. Duringthis time, microprocessor 322 beings the calculation associated withEquations 1-5 and 9 above. At the end of time t1 the microprocessor 322beings a temperature compensation sequence as indicated by block 660 bydriving solenoid PMS with a 100% duty cycle as indicated by block 662.When the time delay T₂ indicated by decision block 666 ends, themicroprocessor 322 follows YES path 668 and reads the actual currentI_(A) at time t2, as indicated by input block 670, and thereaftercompletes the calculation of DC-MAX by using the value I_(A) to finishsolving Equations 9, 3 and 1. Using the just-calculated value forDC-MAX, microprocessor 322 adjusts the duty cycle of the PWM signalsupplied to solenoid PMS to the value specified by DC-MAX, as indicatedin output block 674. While waiting for the reduced pressure clutchengagement time delay T₃ to end, as indicated by decision block 678,microprocessor 322 decrements the duty cycle of the PWM signal appliedto solenoid PMS in accordance with the decay rate DR at 10 millisecondintervals, as is indicated by output block 682 and decision diamond 684.Thus, if the time delay T₃ is 1.5 seconds long, for example, the dutycycle of the PWM signal will be reduced 150 times in accordance with thedecay DR, thus providing a smooth steady increase in clutch engagementpressure as determined by clutch pressure modulation circuit 236 in FIG.5. When time delay T₃ ends, the PWM sequence and shift of thetransmission are complete, as noted in block 686, and accordingly thesolenoid PMS is completely deengerized as indicated in output block 688.

FIG. 17 is a duty cycle vs. time graph very similar to that in FIG. 15which shows an alternative technique for carrying out the PWM sequence.The heavy line 692 represents the average value or duty cycle of PWMsignal applied on line 380 to the driver circuit 350f for solenoid PMS.For the sake of simplicity and ease of understanding FIG. 17, assumethat the transmission 20 is in neutral prior to time t4 and that anupshift request for a forward gear is received at time t4. Accordingly,at time t4 the desired speed clutch and forward directional clutch arecommanded to begin engagement by energizing the solenoid valvessupplying hydraulic fluid to these clutches. In order to take thereading of the actual current through solenoid PMS required forperforming temperature compensation, the solenoid PMS is energized witha 100% duty cycle signal beginning at time t4 and lasting until time t5as indicated by line segment 696. In interval between times t4 and t5corresponds to the time interval T₂ between times t1 and t2 in FIG. 15,and is preferably 80 milliseconds long. At time t5 the solenoid PMS isdeenergized as indicated by line segment 694 to allow the pressurereducing valve 240 to return to its normal full-open position, thusallowing a maximum flow rate therethrough to hydraulic line 272 in orderto permit the directional clutch pack to be engaged to fill quickly withhydraulic fluid. At time t6, this process (which corresponds to timedelay T₁ in FIG. 15) is complete and the clutch pack is ready to beginfrictional engagement. At this point, the solenoid valve PMS is turnedon by providing a PWM signal initially having the value DC-MAX asindicated by point 700 to reduce the hydraulic pressure in hydraulicline 272 to a desired minimal value where the clutch pack of thedirectional clutch just begins to achieve frictional sliding engagement.Thereafter, the hydraulic pressure in line 272 is increased by allowingthe PWM duty cycle to decay as indicated by sloping line segment 702, inthe same manner as in FIG. 15. At time t6, the duty cycle defaults to 0%if it is not already at 0%. The time delay between time t5 and t6corresponds to time delay T₃ in FIG. 15.

The ability of electronic controller 30 to have many values stored inone or more tables, arrays or other data structures in its memory 330and almost instantly access them as needed, makes it possible tocustomize each individual parameter relevant to the operation oftransmission 20 by electronic controller 30 to an optimal value for eachgear shift. In a preferred embodiment of electronic controller 30, atable (or other suitable data storage structure) may be provided toadjust key parameters which do (or may have) a bearing upon thesmoothness of a clutch engagement associated with any particular gearshift. FIG. 18 shows one such table 720 which has seven columns andthirty rows. Table 720 illustrates how key parameters can be customizedfor all conceivable gear shifts which a powershift transmission, such astransmission 20, could experience during normal operation. Columns 1 and2 specify the gear shift associated with a particular row, with column 1representing the state of the transmission before the gear shift, andcolumn 2 representing the state of the transmission after the gearshift. Columns 3 through 6 would normally contain the actual values ofkey parameters to be used by controller 30 during the PWM sequence foreach gear shift of particular transmission/vehicle combination. Theparameters respectively associated with columns 3-6 are: time delay T₁,D_(NSV) (the nominal value for DC-MAX after compensation for magneticcompensation and before compensation for temperature or voltage), decayrate DR, and time delay T₃. In order to more fully illustrate thepresent invention, hypothetical values are shown in columns 3-6. (Theselection of specific values for the parameters in columns 3-6 does notform part of the present invention.)

The first sixteen rows of table 720 are for normal one-gear shifts,either up or down, including shifts into and out of neutral. Rows 17-24are for shuttle-shifts, and rows 25-30 are for skip-shifts. Column 7indicates the number of clutches to be filled with respect to each ofthe gear shifts. For example, the row 1 shift from neutral to first gearforward requires the filling of two clutches, namely forward directionalclutch and the first speed gear clutch 1SC. Each of the shifts in rows2-4 and 6-8 require the filling of only one clutch pack, a speed clutchpack, since the appropriate directional clutch is already filled priorto the gear shift. Row 5 and 13 are included in table 720 only forillustration and completeness, since there is no need to execute the PWMsequence depicted in FIGS. 15 and 16 when shifting to neutral.

In those situations where there are more basic factors which influencethe various values for a key parameter, it may be desirable to calculatethe desired values for the key parameter from those more basic factorsrather than storing values in a table. For example column 7 indicatesthe number of clutches to be filled for each particular gear shiftspecified in a row. If it requires 75 milliseconds to fill one of thedirectional clutches F_(DC) or R_(DC), and only 55 milliseconds to fillone of the smaller speed clutches 1SC-4SC, and the value of time delayT₁ is only base upon the types and numbers of clutches to be filled, thevalue of time delay T₀ could be calculated simply by knowing how manyclutches and which types of clutches are being engaged for anyparticular gear shift. An inspection of columns 3 and 7 will show thatall of the values shown in column 3 can be readily calculated from theforegoing two basic values of 55 milliseconds and 75 milliseconds. In asimilar manner, the nominal starting values D_(NSV) for DC-MAX shown incolumn 4 may be calculated in a simple fashion since all forward shiftsrequire a setting of 75%, while all reverse shifts require a setting of85%. Accordingly, those in the art will appreciate that alternative datastructures and additional formulas may be used for storing and/orcalculating the values of key parameters to be changed with eachindividual gear shift from more basic factors, rather than storing themin a large table like table 720. In any event, by using tables or othersuitable data structures, by themselves or in combination with formulas,such as those provided in Equations 1-9 or other formulas, thecontroller 30 of the present invention may provide for adjustment of anyof the parameters mentioned herein which influence or would helpoptimize the clutch engagement associated with every individual gearshift to which transmission 20 is subjected. Thus, those in the art willappreciate that microprocessor-based controller 30 operating underprogram storage with memory means for the storage of desired values ofkey parameters provides an extremely flexible and easy-to-adjustelectronic control system for powershift transmissions employingproportional actuation devices, such as proportional solenoid valves tomodulate clutch engagement pressure or other hydraulic parameters suchas flow rate.

Simulation Results Illustrating Controller's Utility (FIGS. 19-21)

FIGS. 19 through 21 are graphs showing the hydraulic pressure bearingupon a directional clutch being engaged, vehicle output speed, andtransmission output torque as a function of time. These graphsillustrate the effect of some of the key parameters controlled by thePWM sequence upon transmission 20 and in a simulated vehicleapplication. The graphs of FIGS. 19-21 represent full power reversals orshuttle-shifts from a selected forward gear to a selected reverse gear.The two general criteria established for vehicle response for FIG. 19are: (1) during a direction change the vehicle's acceleration shall beconstant and not exceed 0.3 g's; and (2) there shall be no appreciabletime lag (i.e., a lag greater than 200 milliseconds) between the timethe operator commands a direction change and the time the vehicleresponds.

The data provided in FIGS. 19-21 is from tests of a prototype ofelectronic controller 30 of the present invention in use with aprototype of the Funk 5000 Series transmission (i.e. transmission 20)that was used to drive a flywheel which simulates the inertia of a52,000 pound rubber-tired loader vehicle. In the tests, thetransmission-flywheel combination was operated at a speed that simulatesthe loader traveling at 7 miles per hour in the forward direction andthen being shifted into a reverse direction. FIG. 19 shows, as afunction of time, a curve 740 depicting directional clutch engagementpressure, curve 742 depicting output torque, and a curve 744 depictingsimulated vehicle output speed. In the test associated with FIG. 19, theshift request was received at time t0, at which time solenoid FCS of theforward directional clutch FDC was deenergized, solenoid RCS of thereverse directional clutch RDC was energized, and the solenoid PMS ofvalve 22f was supplied with a PWM signal having a duty cycle ofapproximately 60%. This duty cycle was maintained until time t3 (thatis, for approximately 1.5 seconds) after which time the duty cycle wasallowed to rapidly decay, thereby allowing the clutch pressure to clutchRDC to full recover. Maintaining a constant duty cycle on solenoid PMSprovided a constant clutch pressure as shown in curve portion 740a, andresulted in a nearly constant output torque as shown in portion 742a ofcurve 742. Furthermore, the constant output torque resulted in aconstant flywheel (vehicle) acceleration of 0.27 g's, thus satisfyingthe first criteria.

However, the second criteria was not satisfied. As seen in FIG. 19,approximately 0.6 seconds were required to fill the reverse directionalclutch RDC, and thus begin torque transmittal. In order to decrease thistime lag, the time delay T₁ was provided, so that although thedirectional and speed clutch solenoids were being energized immediatelyupon receipt of the shuttle-shift request at time t0, the solenoid PMSwas not energized until after time delay T₀ (approximately 130milliseconds). By not immediately energizing solenoid PMS, the higherpressure available through hydraulic line 272 filled the directionalclutch RDC at a faster rate. FIG. 20 shows the resulting improvement.

At this point, as a result of parallel testing on an actual vehicle witha prototype of controller 30 and transmission 20, it became apparentthat the first general criteria, namely constant acceleration, requiredmodification. This was due to the fact that the sharp rise in torqueseen at curve portion 742b in FIGS. 19 and 20 up to its "constant value"at curve portion 742a was causing an undesirable jerk. In other words,the rate of change of acceleration was too high. The accelerationcriteria was then modified as follows: (1) the vehicle accelerationduring a directional change shall not exceed 0.5 g's; and (2) the rateof change of vehicle acceleration shall not exceed 0.5 g's per second.In order to meet this modified criteria, the values of parameters (suchas DC-MAX) within the prototype electronic controller 30 were againmodified, and a gradually decreasing duty cycle (namely the decay rateDR) was introduced during time delay T₃ following the time delays T₁ andT₂. By allowing the duty cycle to gradually decrease, a gradual increasein clutch engagement pressure was provided as shown in curve portion750a of clutch pressure curve 750 in FIG. 21. These changes resulted ina gradually increasing output torque as shown in curve 752 and anacceptable output speed response shown in curve 754 of FIG. 20.

FIGS. 19-21 thus demonstrate in a graphic manner the advantages ofutilizing a microprocessor-based electronic controller 30 wherein thevalues of key parameters affecting the clutch engagement process areeasily alterable so that the transmission can be readily tailored to therequirements of different vehicles and applications.

EPILOGUE

While the foregoing detailed description has concerned a powershifttransmission 20 which has four forward gears and four reverse gears,those skilled in the art will appreciate that the teachings of thepresent invention are equally applicable to other powershifttransmissions, such as the Funk 2000 Series transmission which has sixforward gears (and two forward directional clutches), and three reversegears (and one reverse directional clutch). As long as the directional(or other) clutches being engaged have a proportional actuator means,such as clutch pressure modulation circuit including a proportionalsolenoid-operated valve (or an equivalent thereof), the various aspectsof the electronic control system of the present invention may bebeneficially applied to provide smooth clutch engagement by modulatingthe hydraulic pressure of such engagement. Also, while controller 30operated only one proportional actuator means, it may if desired ornecessary be provided with additional PWM signal-generating means tohandle a plurality of proportional actuator means.

In a broader sense, various aspects of the present invention, such asthe temperature compensation and measurement techniques discussedherein, the techniques for compensating for magnetic flux amongstsolenoids, and the voltage compensation schemes, all may beadvantageously utilized with power-transmitting apparatuses used for orin heavy duty off-road vehicles such as farm tractors, road graders andfront-end loaders. For the sake of helping construe the appended claimsand more properly defining the present invention, definitions of severalterms will now be provided.

As used herein the term "power-transmitting apparatus" encompasses:transmission and internal combustion engines of all types (includingthose used in any type of commercially available, self-power land-basedvehicles); implements, power-take-off ("PTO") attachments and any typeof powered accessory for or used in conjunction with a sturdy motorizedvehicle; and hydraulically-operated controls or systems associated withany of the items mentioned above in this sentence.

As used herein, the term "off-road vehicle" includes any mobile vehiclewhich is principally used in the agricultural construction equipment ormining industries. Such off-road vehicles include but are not limited totractors, front-end loaders, back hoes, power shovels, bulldozers, roadgraders, and heavy-duty dump trucks.

As used herein, the term "power shift transmission" includes arelatively heavy-duty power transmission unit having at least onerotatable power input shaft and one rotatable power output shaft whichmay be coupled together in power-transmitting relation by the selectiveengagement of one or more hydraulically actuated clutches and gearsassociated therewith operated by electrically-operated hydraulic valves.

As used herein, the term "electrically-operated hydraulic valves"includes solenoid-operated hydraulic valves or the like which havecoils, electric windings or any other type of electrically actuatedoperators.

As used herein, the term "alternating electrical signal" includes ingeneral pulsating signals having a generally periodic or repetitivewaveform, such as rectangular waveforms, triangular waveforms includingsoft-tooth waveforms, sinusoidal waveforms, and in particular includesthose waveforms which have a net DC component, such as the PWM signalsdiscussed herein.

As used herein, the term "microprocessor means" includesmicroprocessors, microcomputers, and digital electronic systemsutilizing one or more LSI or VLSI integrated circuits operable underprogram control.

The foregoing detailed description shows that the preferred embodimentsof the present invention are well suited to fulfill the objects abovestated. It is recognized that those in the art may make variousmodifications or additions to the preferred embodiments chosen toillustrate the present invention without departing from the spirit andproper scope of the present invention, which is defined by the appendedclaims, including all fair equivalents thereof.

We claim:
 1. An improved electronic control system for use with apowershift transmission having a plurality of hydraulically-actuatedclutches and at least one solenoid-operated hydraulic valve means foradjusting at least one parameter within the transmission, such valvemeans including a solenoid coil to which a first electrical signal isapplied, the electronic control system being of the type which includeselectronic switching means connectable in series with the coil to form aseries combination to which a D.C. supply voltage is applied across, theelectronic control system including microprocessor means for operatingthe powershift transmission in accordance with operating parametersstored in the microprocessor means for:determining the actual value ofthe supply voltage provided across the series combination of thesolenoid coil and the electronic switching means; determining thedifference between the actual value of the supply voltage and apredetermined nominal voltage value of the supply voltage; and adjustingthe second signal in inverse proportion to the value of the difference,thereby compensating for variation in the supply voltage.
 2. A method ofoperating a power-transmitting apparatus used in or with an off-roadvehicle, the apparatus having at least one proportional actuator meansfor adjusting an operating parameter of the apparatus, the actuatormeans including a solenoid coil to which a first signal which is analternating electrical signal is applied, the electronic control systembeing of the type which includes an electronic switching meansconnectable in series with the coil for applying the first signal to thecoil, and control means for generating a second signal representing thedesired operating point of the proportional actuator means, the methodcomprising:providing a direct current (DC) voltage from the normalvehicle electrical power supply system across the series combination ofsolenoid coil and electronic switching means; sensing the actual valueof the DC voltage from the vehicle supply system; determining thedifference between the actual value of the DC voltage and apredetermined nominal voltage value of the DC voltage; and promptlyadjusting the second signal in inverse proportion to the value of thedifference, thereby substantially simultaneously compensating forvariations in the actual DC voltage as such variations occur.
 3. Amethod as in claim 2, wherein the first and second signals are pulsewidth modulated signals and the method further comprises the stepof:generating the second signal by means of a programmable timing meanswhich operates concurrently with and is controlled by the microprocessormeans.